2011-06-09 04:56:17 +08:00
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>pair_style adp command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>pair_style adp
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>pair_style adp
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pair_coeff * * Ta.adp Ta
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pair_coeff * * ../potentials/AlCu.adp Al Al Cu
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Style <I>adp</I> computes pairwise interactions for metals and metal alloys
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using the angular dependent potential (ADP) of <A HREF = "#Mishin">(Mishin)</A>,
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which is a generalization of the <A HREF = "pair_eam.html">embedded atom method (EAM)
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2011-06-20 23:25:04 +08:00
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potential</A>. The LAMMPS implementation is discussed in
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<A HREF = "#Singh">(Singh)</A>. The total energy Ei of an atom I is given by
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2011-06-09 04:56:17 +08:00
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</P>
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<CENTER><IMG SRC = "Eqs/pair_adp.jpg">
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</CENTER>
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<P>where F is the embedding energy which is a function of the atomic
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electron density rho, phi is a pair potential interaction, alpha and
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beta are the element types of atoms I and J, and s and t = 1,2,3 and
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refer to the cartesian coordinates. The mu and lambda terms represent
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the dipole and quadruple distortions of the local atomic environment
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which extend the original EAM framework by introducing angular forces.
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</P>
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<P>Note that unlike for other potentials, cutoffs for ADP potentials are
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not set in the pair_style or pair_coeff command; they are specified in
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the ADP potential files themselves. Likewise, the ADP potential files
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list atomic masses; thus you do not need to use the <A HREF = "mass.html">mass</A>
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command to specify them.
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</P>
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<P>The NIST WWW site distributes and documents ADP potentials:
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</P>
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<PRE>http://www.ctcms.nist.gov/potentials
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</PRE>
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<P>Note that these must be converted into the extended DYNAMO <I>setfl</I>
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format discussed below.
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</P>
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<P>The NIST site is maintained by Chandler Becker (cbecker at nist.gov)
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who is good resource for info on interatomic potentials and file
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formats.
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</P>
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<HR>
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<P>Only a single pair_coeff command is used with the <I>adp</I> style which
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specifies an extended DYNAMO <I>setfl</I> file, which contains information
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for M elements. These are mapped to LAMMPS atom types by specifying N
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additional arguments after the filename in the pair_coeff command,
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where N is the number of LAMMPS atom types:
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</P>
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<UL><LI>filename
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<LI>N element names = mapping of extended <I>setfl</I> elements to atom types
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</UL>
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2011-06-20 23:25:04 +08:00
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<P>As an example, the potentials/AlCu.adp file, included in the
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potentials directory of the LAMMPS distrbution, is an extended <I>setfl</I>
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file which has tabulated ADP values for w elements and their alloy
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interactions: Cu and Al. If your LAMMPS simulation has 4 atoms types
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and you want the 1st 3 to be Al, and the 4th to be Cu, you would use
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the following pair_coeff command:
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</P>
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<PRE>pair_coeff * * AlCu.adp Al Al Al Cu
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</PRE>
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<P>The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
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The first three Al arguments map LAMMPS atom types 1,2,3 to the Al
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element in the extended <I>setfl</I> file. The final Cu argument maps
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LAMMPS atom type 4 to the Al element in the extended <I>setfl</I> file.
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Note that there is no requirement that your simulation use all the
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elements specified by the extended <I>setfl</I> file.
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</P>
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<P>If a mapping value is specified as NULL, the mapping is not performed.
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This can be used when an <I>adp</I> potential is used as part of the
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<I>hybrid</I> pair style. The NULL values are placeholders for atom types
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that will be used with other potentials.
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</P>
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<P><I>Adp</I> files in the <I>potentials</I> directory of the LAMMPS distribution
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have an ".adp" suffix. A DYNAMO <I>setfl</I> file extended for ADP is
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formatted as follows. Basically it is the standard <I>setfl</I> format
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with additional tabulated functions u and w added to the file after
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the tabulated pair potentials. See the <A HREF = "pair_eam.html">pair_eam</A>
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command for further details on the <I>setfl</I> format.
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</P>
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<UL><LI>lines 1,2,3 = comments (ignored)
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<LI>line 4: Nelements Element1 Element2 ... ElementN
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<LI>line 5: Nrho, drho, Nr, dr, cutoff
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</UL>
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<P>Following the 5 header lines are Nelements sections, one for each
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element, each with the following format:
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</P>
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<UL><LI>line 1 = atomic number, mass, lattice constant, lattice type (e.g. FCC)
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<LI>embedding function F(rho) (Nrho values)
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<LI>density function rho(r) (Nr values)
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</UL>
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<P>Following the Nelements sections, Nr values for each pair potential
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phi(r) array are listed for all i,j element pairs in the same format
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as other arrays. Since these interactions are symmetric (i,j = j,i)
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only phi arrays with i >= j are listed, in the following order: i,j =
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(1,1), (2,1), (2,2), (3,1), (3,2), (3,3), (4,1), ..., (Nelements,
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Nelements).
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</P>
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<P>After the phi(r) arrays, each of the u(r) arrays are listed in the
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same order with the same assumptions of symmetry. Directly following
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the u(r), the w(r) arrays are listed.
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</P>
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<HR>
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
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</P>
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<P>For atom type pairs I,J and I != J, where types I and J correspond to
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two different element types, no special mixing rules are needed, since
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the ADP potential files specify alloy interactions explicitly.
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</P>
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<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
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shift, table, and tail options.
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</P>
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<P>This pair style does not write its information to <A HREF = "restart.html">binary restart
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files</A>, since it is stored in tabulated potential files.
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Thus, you need to re-specify the pair_style and pair_coeff commands in
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an input script that reads a restart file.
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</P>
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<P>This pair style can only be used via the <I>pair</I> keyword of the
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<A HREF = "run_style.html">run_style respa</A> command. It does not support the
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<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
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</P>
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<HR>
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<P><B>Restrictions:</B>
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</P>
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<P>This pair style is part of the "manybody" package. It is only enabled
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if LAMMPS was built with that package (which it is by default).
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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 = "pair_coeff.html">pair_coeff</A>, <A HREF = "pair_eam.html">pair_eam</A>
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</P>
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<P><B>Default:</B> none
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</P>
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<HR>
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2011-06-20 23:25:04 +08:00
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<A NAME = "Mishin"></A>
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<P><B>(Mishin)</B> Mishin, Mehl, and Papaconstantopoulos, Acta Mater, 53, 4029
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(2005).
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</P>
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<A NAME = "Singh"></A>
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<P><B>(Singh)</B> Singh and Warner, Acta Mater, 58, 5797-5805 (2010),
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</P>
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</HTML>
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