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doc/fix_qeq.html
184
doc/fix_qeq.html
|
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@ -19,7 +19,7 @@
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID style Nevery cutoff tolerance maxiter params
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<PRE>fix ID group-ID style Nevery cutoff tolerance maxiter qfile
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>style = <I>qeq/point</I> or <I>qeq/shielded</I> or <I>qeq/slater</I> or <I>qeq/dynamic</I>
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@ -27,7 +27,7 @@
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<LI>cutoff = global cutoff for charge-charge interactions (distance unit)
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<LI>tolerance = precision to which charges will be equilibrated
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<LI>maxiter = maximum iterations to perform charge equilibration
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<LI>params = a filename
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<LI>qfile = a filename with QEq parameters
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</UL>
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<P><B>Examples:</B>
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</P>
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@ -39,117 +39,129 @@ fix 1 qeq qeq/dynamic 1 12 1.0e-3 100 my_qeq
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<P><B>Description:</B>
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</P>
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<P>Perform the charge equilibration (QEq) method as described in <A HREF = "#Rappe">(Rappe
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and Goddard)</A> and formulated in <A HREF = "#Nakano">(Nakano)</A> (also
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known as the matrix inversion method)
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and in <A HREF = "#Rick">(Rick and Stuart)</A> (also known as the extended
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Lagrangian method) based on the electronegativity equilization principle.
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These fixes can be used with any potential in LAMMPS, so long as it defines and
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uses charges on each atom and that QEq parameters are provided.
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and Goddard)</A> and formulated in <A HREF = "#Nakano">(Nakano)</A> (also known
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as the matrix inversion method) and in <A HREF = "#Rick">(Rick and Stuart)</A> (also
|
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known as the extended Lagrangian method) based on the
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electronegativity equilization principle. These fixes can be used
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with any potential in LAMMPS, so long as it defines and uses charges
|
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on each atom and that QEq parameters are provided.
|
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</P>
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<P>IMPORTANT NOTE: The <A HREF = "fix_qeq_comb.html">fix qeq/comb</A>
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command should be used to perform charge equliibration with the <A HREF = "pair_comb.html">COMB
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<P>IMPORTANT NOTE: The <A HREF = "fix_qeq_comb.html">fix qeq/comb</A> command must
|
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still be used to perform charge equliibration with the <A HREF = "pair_comb.html">COMB
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||||
potential</A>. The <A HREF = "fix_qeq_reax.html">fix qeq/reax</A>
|
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command can be used to perform charge equilibration with the <A HREF = "pair_reax_c.html">ReaxFF force
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||||
field</A>, although fix qeq/shielded yields exact same
|
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results as fix qeq/reax if <I>Nevery</I>, cutoff</I>, and <I>tolerance</I> are the same.
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command can be used to perform charge equilibration with the <A HREF = "pair_reax_c.html">ReaxFF
|
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force field</A>, although fix qeq/shielded yields the
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same results as fix qeq/reax if <I>Nevery</I>, cutoff</I>, and <I>tolerance</I> are
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the same. Eventually the fix qeq/reax command will be deprecated.
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</P>
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<P>The QEq method minimizes the electrostatic energy of the system (or
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equalizes the derivative of energy with respect to charge of all the
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atoms) by adjusting the partial charge on individual atoms based on
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interactions with their neighbors within <I>cutoff</I>.
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It reqires some parameters for each atom type provided in a file
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specified by <I>params</I>. First line of the file should be the unit
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style of these parameters. These
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fixes support real, metal, si, cgs, and electron units. Using lj,
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micro, and nano units will result in an error.
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Each of the following lines should be formatted as follows:
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<P>The QEq method minimizes the electrostatic energy of the system (or
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equalizes the derivative of energy with respect to charge of all the
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atoms) by adjusting the partial charge on individual atoms based on
|
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interactions with their neighbors within <I>cutoff</I>. It reqires a few
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parameters for each atom type which provided in a file specified by
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<I>qfile</I>. The file has the following format
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</P>
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<PRE>itype chi eta gamma zeta qcore
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<PRE>units
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1 chi eta gamma zeta qcore
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2 chi eta gamma zeta qcore
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...
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Ntype chi eta gamma zeta qcore
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</PRE>
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<P>where <I>itype</I> is the atom type from 1 to Ntypes, <I>chi</I> denotes the
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electronegativity in energy units, <I>eta</I> denotes the self-Coulomb
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potential in energy units, <I>gamma</I> denotes the shielded Coulomb
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constant defined by <A HREF = "#vanDuin">ReaxFF force field</A> in distance units,
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<I>zeta</I> denotes the Slater type orbital exponent defined by the
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<A HREF = "#Streitz">Streitz-Mintmire</A> potential (not yet available in LAMMPS)
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in reverse distance units, and <I>qcore</I> denotes the charge of the
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nucleus defined by the Streitz-Mintmire potential in charge units.
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<P>The first line of the file specifies the units for these parameters,
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as explained on the <A HREF = "units.html">units</A> command doc page. Currently,
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only the following units are supported: real, metal, si, cgs,
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electron. Using other units (lj, micro, nano) will result in an error.
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</P>
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<P>The <I>qeq/point</I> style describes partial charges on atoms as point charges.
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Interaction between a pair of charged particles is 1/r, which is the simplest
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description of the interaction between charges. Only <I>chi</I> and <I>eta</I>
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parameters in the <I>params</I> file are used. Note that Coulomb catastrophe
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can occur if repulsion between the pair of charged particles is too weak.
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This style solves partial charges on atoms via the matrix inversion method.
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A tolerance of 1.0e-6 is usually a good number.
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<P>Then there is one line per atom type with the following parameters.
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Only a subset of the parameters is used by each QEq style as descibed
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below, thus the others can be set to 0.0 if desired.
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</P>
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<P>The <I>qeq/shielded</I> style describes partial charges on atoms also as point
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charges, but uses a shielded Coulomb potential to describe
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the interaction between a pair of charged particles. Interaction through
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the shielded Coulomb is given by equation (13) of the
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<A HREF = "#vanDuin">ReaxFF force field</A> paper. The shielding accounts for charge overlap
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between charged particles at small separation. This style is the same as
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<A HREF = "fix_qeq_reax.html">fix qeq/reax</A>, and can be used with
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<A HREF = "pair_reax_c.html">pair_style reax/c</A>. Only <I>chi</I>, <I>eta</I>, and <I>gamma</I> parameters
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in the <I>params</I> file are used.
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This style solves partial charges on atoms via the matrix inversion method.
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A tolerance of 1.0e-6 is usually a good number.
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<UL><LI><I>chi</I> = electronegativity in energy units
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<LI><I>eta</I> = self-Coulomb potential in energy units
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<LI><I>gamma</I> = shielded Coulomb constant defined by <A HREF = "#vanDuin">ReaxFF force field</A> in distance units
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<LI><I>zeta</I> = Slater type orbital exponent defined by the <A HREF = "#Streitz">Streitz-Mintmire</A> potential in reverse distance units
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<LI><I>qcore</I> = charge of the nucleus defined by the <A HREF = "#Streitz">Streitz-Mintmire potential</A> potential in charge units
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</UL>
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<P>The <I>qeq/point</I> style describes partial charges on atoms as point
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charges. Interaction between a pair of charged particles is 1/r,
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which is the simplest description of the interaction between charges.
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Only the <I>chi</I> and <I>eta</I> parameters from the <I>qfile</I> file are used.
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Note that Coulomb catastrophe can occur if repulsion between the pair
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of charged particles is too weak. This style solves partial charges
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on atoms via the matrix inversion method. A tolerance of 1.0e-6 is
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usually a good number.
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</P>
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<P>The <I>qeq/slater</I> style describes partial charges on atoms as spherical
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charge densities centered around atoms via the Slater 1<I>s</I> orbital, so that
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the interaction between a pair of charged particles is the product of two
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Slater 1<I>s</I> orbitals. The expression for the Slater 1<I>s</I> orbital is given under
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equation (6) of the <A HREF = "#Streitz">Streitz-Mintmire</A> paper. <I>chi</I>, <I>eta</I>, <I>zeta</I>,
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and <I>qcore</I> parameters in the <I>params</I> file are used.
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This style solves partial charges on atoms via the matrix inversion method.
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A tolerance of 1.0e-6 is usually a good number.
|
||||
<P>The <I>qeq/shielded</I> style describes partial charges on atoms also as
|
||||
point charges, but uses a shielded Coulomb potential to describe the
|
||||
interaction between a pair of charged particles. Interaction through
|
||||
the shielded Coulomb is given by equation (13) of the <A HREF = "#vanDuin">ReaxFF force
|
||||
field</A> paper. The shielding accounts for charge overlap
|
||||
between charged particles at small separation. This style is the same
|
||||
as <A HREF = "fix_qeq_reax.html">fix qeq/reax</A>, and can be used with <A HREF = "pair_reax_c.html">pair_style
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||||
reax/c</A>. Only the <I>chi</I>, <I>eta</I>, and <I>gamma</I>
|
||||
parameters from the <I>qfile</I> file are used. This style solves partial
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charges on atoms via the matrix inversion method. A tolerance of
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1.0e-6 is usually a good number.
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||||
</P>
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||||
<P>The <I>qeq/dynamic</I> style describes partial charges on atoms as point charges
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that interact through 1/r, but the extended Lagrangian method is used to solve
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partial charges on atoms. Only <I>chi</I> and <I>eta</I> parameters in the <I>params</I> file
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are used. Note that Coulomb catastrophe can occur if repulsion between the
|
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pair of charged particles is too weak.
|
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A tolerance of 1.0e-3 is usually a good number.
|
||||
<P>The <I>qeq/slater</I> style describes partial charges on atoms as spherical
|
||||
charge densities centered around atoms via the Slater 1<I>s</I> orbital, so
|
||||
that the interaction between a pair of charged particles is the
|
||||
product of two Slater 1<I>s</I> orbitals. The expression for the Slater
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1<I>s</I> orbital is given under equation (6) of the
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<A HREF = "#Streitz">Streitz-Mintmire</A> paper. Only the <I>chi</I>, <I>eta</I>, <I>zeta</I>, and
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<I>qcore</I> parameters from the <I>qfile</I> file are used. This style solves
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||||
partial charges on atoms via the matrix inversion method. A tolerance
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||||
of 1.0e-6 is usually a good number.
|
||||
</P>
|
||||
<P>Note that <I>qeq/point</I>, <I>qeq/shielded</I>, and <I>qeq/slater</I> describe different charge
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models, whereas the matrix inversion method and the extended Lagrangian method
|
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(<I>qeq/dynamic</I>) are different solvers.
|
||||
<P>The <I>qeq/dynamic</I> style describes partial charges on atoms as point
|
||||
charges that interact through 1/r, but the extended Lagrangian method
|
||||
is used to solve partial charges on atoms. Only the <I>chi</I> and <I>eta</I>
|
||||
parameters from the <I>qfile</I> file are used. Note that Coulomb
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||||
catastrophe can occur if repulsion between the pair of charged
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||||
particles is too weak. A tolerance of 1.0e-3 is usually a good
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||||
number.
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</P>
|
||||
<P>Note that the <I>qeq/point</I> and the <I>qeq/dynamic</I> styles both describe charges as
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point charges that interact through 1/r relationship, but solve partial charges
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||||
on atoms using different solvers. <I>qeq/point</I> and the <I>qeq/dynamic</I> styles should
|
||||
yield comparable results if the QEq parameters and <I>Nevery</I>, cutoff</I>,
|
||||
and <I>tolerance</I> are the same. <I>qeq/point</I> is typically faster, but <I>qeq/dynamic</I>
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||||
scales better on larger sizes.
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||||
<P>Note that <I>qeq/point</I>, <I>qeq/shielded</I>, and <I>qeq/slater</I> describe
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different charge models, whereas the matrix inversion method and the
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extended Lagrangian method (<I>qeq/dynamic</I>) are different solvers.
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</P>
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<P>IMPORTANT NOTE: To avoid the evaluation of the derivative of charge with
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respect to position, which is typically ill-defined, the system should have a
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zero net charge.
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||||
<P>Note that the <I>qeq/point</I> and the <I>qeq/dynamic</I> styles both describe
|
||||
charges as point charges that interact through 1/r relationship, but
|
||||
solve partial charges on atoms using different solvers. <I>qeq/point</I>
|
||||
and the <I>qeq/dynamic</I> styles should yield comparable results if the
|
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QEq parameters and <I>Nevery</I>, cutoff</I>, and <I>tolerance</I> are the same.
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<I>qeq/point</I> is typically faster, but <I>qeq/dynamic</I> scales better on
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larger sizes.
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</P>
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<P>IMPORTANT NOTE: Developing QEq parameters (chi, eta, gamma, zeta, and qcore)
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is an "art". Charges on atoms are not guaranteed to equilibrate with arbitrary
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choices of these parameters. We do not develop these QEq paramters.
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<P>IMPORTANT NOTE: To avoid the evaluation of the derivative of charge
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||||
with respect to position, which is typically ill-defined, the system
|
||||
should have a zero net charge.
|
||||
</P>
|
||||
<P>IMPORTANT NOTE: Developing QEq parameters (chi, eta, gamma, zeta, and
|
||||
qcore) is an "art". Charges on atoms are not guaranteed to
|
||||
equilibrate with arbitrary choices of these parameters. We do not
|
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develop these QEq paramters.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>No information about these fixes is written to <A HREF = "restart.html">binary restart
|
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files</A>. No global scalar or vector or per-atom
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quantities are stored by these fixes for access by various <A HREF = "Section_howto.html#howto_15">output
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commands</A>. No parameter of these fixes can
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be used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A> command.
|
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commands</A>. No parameter of these fixes
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||||
can be used with the <I>start/stop</I> keywords of the <A HREF = "run.html">run</A>
|
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command.
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</P>
|
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<P>Thexe fixes are invoked during <A HREF = "minimize.html">energy minimization</A>.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>These fixes are part of the USER-QEQ package. They are only enabled if
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<P>These fixes are part of the QEQ package. They are only enabled if
|
||||
LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
|
||||
LAMMPS</A> section for more info.
|
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</P>
|
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<P><B>Related commands:</B>
|
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</P>
|
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<P><A HREF = "fix_qeq_reax.html">fix qeq/reax</A>
|
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<A HREF = "fix_qeq_comb.html">fix qeq/comb</A>
|
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<P><A HREF = "fix_qeq_reax.html">fix qeq/reax</A>, <A HREF = "fix_qeq_comb.html">fix qeq/comb</A>
|
||||
</P>
|
||||
<P><B>Default:</B> none
|
||||
</P>
|
||||
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|
@ -157,8 +169,8 @@ LAMMPS</A> section for more info.
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|||
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<A NAME = "Rappe"></A>
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<P><B>(Rappe and Goddard)</B> A. K. Rappe and W. A. Goddard III, J Physical Chemistry, 105,
|
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3358-3363 (1991).
|
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<P><B>(Rappe and Goddard)</B> A. K. Rappe and W. A. Goddard III, J Physical
|
||||
Chemistry, 105, 3358-3363 (1991).
|
||||
</P>
|
||||
<A NAME = "Nakano"></A>
|
||||
|
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|
|
|
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184
doc/fix_qeq.txt
184
doc/fix_qeq.txt
|
|
@ -13,7 +13,7 @@ fix qeq/dynamic command :h3
|
|||
|
||||
[Syntax:]
|
||||
|
||||
fix ID group-ID style Nevery cutoff tolerance maxiter params :pre
|
||||
fix ID group-ID style Nevery cutoff tolerance maxiter qfile :pre
|
||||
|
||||
ID, group-ID are documented in "fix"_fix.html command
|
||||
style = {qeq/point} or {qeq/shielded} or {qeq/slater} or {qeq/dynamic}
|
||||
|
|
@ -21,7 +21,7 @@ Nevery = perform charge equilibration every this many steps
|
|||
cutoff = global cutoff for charge-charge interactions (distance unit)
|
||||
tolerance = precision to which charges will be equilibrated
|
||||
maxiter = maximum iterations to perform charge equilibration
|
||||
params = a filename :ul
|
||||
qfile = a filename with QEq parameters :ul
|
||||
|
||||
[Examples:]
|
||||
|
||||
|
|
@ -33,125 +33,137 @@ fix 1 qeq qeq/dynamic 1 12 1.0e-3 100 my_qeq :pre
|
|||
[Description:]
|
||||
|
||||
Perform the charge equilibration (QEq) method as described in "(Rappe
|
||||
and Goddard)"_#Rappe and formulated in "(Nakano)"_#Nakano (also
|
||||
known as the matrix inversion method)
|
||||
and in "(Rick and Stuart)"_#Rick (also known as the extended
|
||||
Lagrangian method) based on the electronegativity equilization principle.
|
||||
These fixes can be used with any potential in LAMMPS, so long as it defines and
|
||||
uses charges on each atom and that QEq parameters are provided.
|
||||
and Goddard)"_#Rappe and formulated in "(Nakano)"_#Nakano (also known
|
||||
as the matrix inversion method) and in "(Rick and Stuart)"_#Rick (also
|
||||
known as the extended Lagrangian method) based on the
|
||||
electronegativity equilization principle. These fixes can be used
|
||||
with any potential in LAMMPS, so long as it defines and uses charges
|
||||
on each atom and that QEq parameters are provided.
|
||||
|
||||
IMPORTANT NOTE: The "fix qeq/comb"_fix_qeq_comb.html
|
||||
command should be used to perform charge equliibration with the "COMB
|
||||
IMPORTANT NOTE: The "fix qeq/comb"_fix_qeq_comb.html command must
|
||||
still be used to perform charge equliibration with the "COMB
|
||||
potential"_pair_comb.html. The "fix qeq/reax"_fix_qeq_reax.html
|
||||
command can be used to perform charge equilibration with the "ReaxFF force
|
||||
field"_pair_reax_c.html, although fix qeq/shielded yields exact same
|
||||
results as fix qeq/reax if {Nevery}, cutoff}, and {tolerance} are the same.
|
||||
command can be used to perform charge equilibration with the "ReaxFF
|
||||
force field"_pair_reax_c.html, although fix qeq/shielded yields the
|
||||
same results as fix qeq/reax if {Nevery}, cutoff}, and {tolerance} are
|
||||
the same. Eventually the fix qeq/reax command will be deprecated.
|
||||
|
||||
The QEq method minimizes the electrostatic energy of the system (or
|
||||
equalizes the derivative of energy with respect to charge of all the
|
||||
atoms) by adjusting the partial charge on individual atoms based on
|
||||
interactions with their neighbors within {cutoff}.
|
||||
It reqires some parameters for each atom type provided in a file
|
||||
specified by {params}. First line of the file should be the unit
|
||||
style of these parameters. These
|
||||
fixes support real, metal, si, cgs, and electron units. Using lj,
|
||||
micro, and nano units will result in an error.
|
||||
Each of the following lines should be formatted as follows:
|
||||
The QEq method minimizes the electrostatic energy of the system (or
|
||||
equalizes the derivative of energy with respect to charge of all the
|
||||
atoms) by adjusting the partial charge on individual atoms based on
|
||||
interactions with their neighbors within {cutoff}. It reqires a few
|
||||
parameters for each atom type which provided in a file specified by
|
||||
{qfile}. The file has the following format
|
||||
|
||||
itype chi eta gamma zeta qcore :pre
|
||||
units
|
||||
1 chi eta gamma zeta qcore
|
||||
2 chi eta gamma zeta qcore
|
||||
...
|
||||
Ntype chi eta gamma zeta qcore :pre
|
||||
|
||||
where {itype} is the atom type from 1 to Ntypes, {chi} denotes the
|
||||
electronegativity in energy units, {eta} denotes the self-Coulomb
|
||||
potential in energy units, {gamma} denotes the shielded Coulomb
|
||||
constant defined by "ReaxFF force field"_#vanDuin in distance units,
|
||||
{zeta} denotes the Slater type orbital exponent defined by the
|
||||
"Streitz-Mintmire"_#Streitz potential (not yet available in LAMMPS)
|
||||
in reverse distance units, and {qcore} denotes the charge of the
|
||||
nucleus defined by the Streitz-Mintmire potential in charge units.
|
||||
The first line of the file specifies the units for these parameters,
|
||||
as explained on the "units"_units.html command doc page. Currently,
|
||||
only the following units are supported: real, metal, si, cgs,
|
||||
electron. Using other units (lj, micro, nano) will result in an error.
|
||||
|
||||
The {qeq/point} style describes partial charges on atoms as point charges.
|
||||
Interaction between a pair of charged particles is 1/r, which is the simplest
|
||||
description of the interaction between charges. Only {chi} and {eta}
|
||||
parameters in the {params} file are used. Note that Coulomb catastrophe
|
||||
can occur if repulsion between the pair of charged particles is too weak.
|
||||
This style solves partial charges on atoms via the matrix inversion method.
|
||||
A tolerance of 1.0e-6 is usually a good number.
|
||||
Then there is one line per atom type with the following parameters.
|
||||
Only a subset of the parameters is used by each QEq style as descibed
|
||||
below, thus the others can be set to 0.0 if desired.
|
||||
|
||||
The {qeq/shielded} style describes partial charges on atoms also as point
|
||||
charges, but uses a shielded Coulomb potential to describe
|
||||
the interaction between a pair of charged particles. Interaction through
|
||||
the shielded Coulomb is given by equation (13) of the
|
||||
"ReaxFF force field"_#vanDuin paper. The shielding accounts for charge overlap
|
||||
between charged particles at small separation. This style is the same as
|
||||
"fix qeq/reax"_fix_qeq_reax.html, and can be used with
|
||||
"pair_style reax/c"_pair_reax_c.html. Only {chi}, {eta}, and {gamma} parameters
|
||||
in the {params} file are used.
|
||||
This style solves partial charges on atoms via the matrix inversion method.
|
||||
A tolerance of 1.0e-6 is usually a good number.
|
||||
{chi} = electronegativity in energy units
|
||||
{eta} = self-Coulomb potential in energy units
|
||||
{gamma} = shielded Coulomb constant defined by "ReaxFF force field"_#vanDuin in distance units
|
||||
{zeta} = Slater type orbital exponent defined by the "Streitz-Mintmire"_#Streitz potential in reverse distance units
|
||||
{qcore} = charge of the nucleus defined by the "Streitz-Mintmire potential"_#Streitz potential in charge units :ul
|
||||
|
||||
The {qeq/slater} style describes partial charges on atoms as spherical
|
||||
charge densities centered around atoms via the Slater 1{s} orbital, so that
|
||||
the interaction between a pair of charged particles is the product of two
|
||||
Slater 1{s} orbitals. The expression for the Slater 1{s} orbital is given under
|
||||
equation (6) of the "Streitz-Mintmire"_#Streitz paper. {chi}, {eta}, {zeta},
|
||||
and {qcore} parameters in the {params} file are used.
|
||||
This style solves partial charges on atoms via the matrix inversion method.
|
||||
A tolerance of 1.0e-6 is usually a good number.
|
||||
The {qeq/point} style describes partial charges on atoms as point
|
||||
charges. Interaction between a pair of charged particles is 1/r,
|
||||
which is the simplest description of the interaction between charges.
|
||||
Only the {chi} and {eta} parameters from the {qfile} file are used.
|
||||
Note that Coulomb catastrophe can occur if repulsion between the pair
|
||||
of charged particles is too weak. This style solves partial charges
|
||||
on atoms via the matrix inversion method. A tolerance of 1.0e-6 is
|
||||
usually a good number.
|
||||
|
||||
The {qeq/dynamic} style describes partial charges on atoms as point charges
|
||||
that interact through 1/r, but the extended Lagrangian method is used to solve
|
||||
partial charges on atoms. Only {chi} and {eta} parameters in the {params} file
|
||||
are used. Note that Coulomb catastrophe can occur if repulsion between the
|
||||
pair of charged particles is too weak.
|
||||
A tolerance of 1.0e-3 is usually a good number.
|
||||
The {qeq/shielded} style describes partial charges on atoms also as
|
||||
point charges, but uses a shielded Coulomb potential to describe the
|
||||
interaction between a pair of charged particles. Interaction through
|
||||
the shielded Coulomb is given by equation (13) of the "ReaxFF force
|
||||
field"_#vanDuin paper. The shielding accounts for charge overlap
|
||||
between charged particles at small separation. This style is the same
|
||||
as "fix qeq/reax"_fix_qeq_reax.html, and can be used with "pair_style
|
||||
reax/c"_pair_reax_c.html. Only the {chi}, {eta}, and {gamma}
|
||||
parameters from the {qfile} file are used. This style solves partial
|
||||
charges on atoms via the matrix inversion method. A tolerance of
|
||||
1.0e-6 is usually a good number.
|
||||
|
||||
Note that {qeq/point}, {qeq/shielded}, and {qeq/slater} describe different charge
|
||||
models, whereas the matrix inversion method and the extended Lagrangian method
|
||||
({qeq/dynamic}) are different solvers.
|
||||
The {qeq/slater} style describes partial charges on atoms as spherical
|
||||
charge densities centered around atoms via the Slater 1{s} orbital, so
|
||||
that the interaction between a pair of charged particles is the
|
||||
product of two Slater 1{s} orbitals. The expression for the Slater
|
||||
1{s} orbital is given under equation (6) of the
|
||||
"Streitz-Mintmire"_#Streitz paper. Only the {chi}, {eta}, {zeta}, and
|
||||
{qcore} parameters from the {qfile} file are used. This style solves
|
||||
partial charges on atoms via the matrix inversion method. A tolerance
|
||||
of 1.0e-6 is usually a good number.
|
||||
|
||||
Note that the {qeq/point} and the {qeq/dynamic} styles both describe charges as
|
||||
point charges that interact through 1/r relationship, but solve partial charges
|
||||
on atoms using different solvers. {qeq/point} and the {qeq/dynamic} styles should
|
||||
yield comparable results if the QEq parameters and {Nevery}, cutoff},
|
||||
and {tolerance} are the same. {qeq/point} is typically faster, but {qeq/dynamic}
|
||||
scales better on larger sizes.
|
||||
The {qeq/dynamic} style describes partial charges on atoms as point
|
||||
charges that interact through 1/r, but the extended Lagrangian method
|
||||
is used to solve partial charges on atoms. Only the {chi} and {eta}
|
||||
parameters from the {qfile} file are used. Note that Coulomb
|
||||
catastrophe can occur if repulsion between the pair of charged
|
||||
particles is too weak. A tolerance of 1.0e-3 is usually a good
|
||||
number.
|
||||
|
||||
IMPORTANT NOTE: To avoid the evaluation of the derivative of charge with
|
||||
respect to position, which is typically ill-defined, the system should have a
|
||||
zero net charge.
|
||||
Note that {qeq/point}, {qeq/shielded}, and {qeq/slater} describe
|
||||
different charge models, whereas the matrix inversion method and the
|
||||
extended Lagrangian method ({qeq/dynamic}) are different solvers.
|
||||
|
||||
IMPORTANT NOTE: Developing QEq parameters (chi, eta, gamma, zeta, and qcore)
|
||||
is an "art". Charges on atoms are not guaranteed to equilibrate with arbitrary
|
||||
choices of these parameters. We do not develop these QEq paramters.
|
||||
Note that the {qeq/point} and the {qeq/dynamic} styles both describe
|
||||
charges as point charges that interact through 1/r relationship, but
|
||||
solve partial charges on atoms using different solvers. {qeq/point}
|
||||
and the {qeq/dynamic} styles should yield comparable results if the
|
||||
QEq parameters and {Nevery}, cutoff}, and {tolerance} are the same.
|
||||
{qeq/point} is typically faster, but {qeq/dynamic} scales better on
|
||||
larger sizes.
|
||||
|
||||
IMPORTANT NOTE: To avoid the evaluation of the derivative of charge
|
||||
with respect to position, which is typically ill-defined, the system
|
||||
should have a zero net charge.
|
||||
|
||||
IMPORTANT NOTE: Developing QEq parameters (chi, eta, gamma, zeta, and
|
||||
qcore) is an "art". Charges on atoms are not guaranteed to
|
||||
equilibrate with arbitrary choices of these parameters. We do not
|
||||
develop these QEq paramters.
|
||||
|
||||
[Restart, fix_modify, output, run start/stop, minimize info:]
|
||||
|
||||
No information about these fixes is written to "binary restart
|
||||
files"_restart.html. No global scalar or vector or per-atom
|
||||
quantities are stored by these fixes for access by various "output
|
||||
commands"_Section_howto.html#howto_15. No parameter of these fixes can
|
||||
be used with the {start/stop} keywords of the "run"_run.html command.
|
||||
commands"_Section_howto.html#howto_15. No parameter of these fixes
|
||||
can be used with the {start/stop} keywords of the "run"_run.html
|
||||
command.
|
||||
|
||||
Thexe fixes are invoked during "energy minimization"_minimize.html.
|
||||
|
||||
[Restrictions:]
|
||||
|
||||
These fixes are part of the USER-QEQ package. They are only enabled if
|
||||
These fixes are part of the QEQ package. They are only enabled if
|
||||
LAMMPS was built with that package. See the "Making
|
||||
LAMMPS"_Section_start.html#start_3 section for more info.
|
||||
|
||||
[Related commands:]
|
||||
|
||||
"fix qeq/reax"_fix_qeq_reax.html
|
||||
"fix qeq/comb"_fix_qeq_comb.html
|
||||
"fix qeq/reax"_fix_qeq_reax.html, "fix qeq/comb"_fix_qeq_comb.html
|
||||
|
||||
[Default:] none
|
||||
|
||||
:line
|
||||
|
||||
:link(Rappe)
|
||||
[(Rappe and Goddard)] A. K. Rappe and W. A. Goddard III, J Physical Chemistry, 105,
|
||||
3358-3363 (1991).
|
||||
[(Rappe and Goddard)] A. K. Rappe and W. A. Goddard III, J Physical
|
||||
Chemistry, 105, 3358-3363 (1991).
|
||||
|
||||
:link(Nakano)
|
||||
[(Nakano)] A. Nakano, Computer Physics Communications, 104, 59-69 (1997).
|
||||
|
|
|
|||
Loading…
Reference in New Issue