2007-01-30 07:28:45 +08:00
|
|
|
<HTML>
|
|
|
|
|
<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>
|
|
|
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<H3>pair_style meam command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
2007-06-05 08:17:19 +08:00
|
|
|
<PRE>pair_style meam
|
2007-01-30 07:28:45 +08:00
|
|
|
</PRE>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>pair_style meam
|
|
|
|
|
pair_coeff * * ../potentials/library.meam Si ../potentials/si.meam Si
|
|
|
|
|
pair_coeff * * ../potentials/library.meam Ni Al NULL Ni Al Ni Ni
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Style <I>meam</I> computes pairwise interactions for a variety of materials
|
|
|
|
|
using modified embedded-atom method (MEAM) potentials
|
|
|
|
|
<A HREF = "#Baskes">(Baskes)</A>. Conceptually, it is an extension to the original
|
2007-02-10 05:40:32 +08:00
|
|
|
<A HREF = "pair_eam.html">EAM potentials</A> which adds angular forces. It is
|
2007-01-30 07:28:45 +08:00
|
|
|
thus suitable for modeling metals and alloys with fcc, bcc, hcp and
|
|
|
|
|
diamond cubic structures, as well as covalently bonded materials like
|
|
|
|
|
silicon and carbon.
|
|
|
|
|
</P>
|
|
|
|
|
<P>In the MEAM formulation, the total energy E of a system of atoms is
|
|
|
|
|
given by:
|
|
|
|
|
</P>
|
|
|
|
|
<CENTER><IMG SRC = "Eqs/pair_meam.jpg">
|
|
|
|
|
</CENTER>
|
|
|
|
|
<P>where F is the embedding energy which is a function of the atomic
|
|
|
|
|
electron density rho, and phi is a pair potential interaction. The
|
|
|
|
|
pair interaction is summed over all neighbors J of atom I within the
|
|
|
|
|
cutoff distance. As with EAM, the multi-body nature of the MEAM
|
|
|
|
|
potential is a result of the embedding energy term. Details of the
|
|
|
|
|
computation of the embedding and pair energies, as implemented in
|
|
|
|
|
LAMMPS, are given in <A HREF = "#Gullet">(Gullet)</A> and references therein.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The various parameters in the MEAM formulas are listed in two files
|
|
|
|
|
which are specified by the <A HREF = "pair_coeff.html">pair_coeff</A> command.
|
|
|
|
|
These are ASCII text files in a format consistent with other MD codes
|
|
|
|
|
that implement MEAM potentials, such as the serial DYNAMO code and
|
|
|
|
|
Warp. Several MEAM potential files with parameters for different
|
|
|
|
|
materials are included in the "potentials" directory of the LAMMPS
|
2007-02-10 05:40:32 +08:00
|
|
|
distribution with a ".meam" suffix. All of these are parameterized in
|
2007-01-30 07:28:45 +08:00
|
|
|
terms of LAMMPS <A HREF = "units.html">metal units</A>.
|
|
|
|
|
</P>
|
|
|
|
|
<P>Note that unlike for other potentials, cutoffs for MEAM potentials are
|
|
|
|
|
not set in the pair_style or pair_coeff command; they are specified in
|
|
|
|
|
the MEAM potential files themselves.
|
|
|
|
|
</P>
|
|
|
|
|
<P>Only a single pair_coeff command is used with the <I>meam</I> style which
|
|
|
|
|
specifies two MEAM files and the element(s) to extract information
|
|
|
|
|
for. The MEAM elements are mapped to LAMMPS atom types by specifying
|
|
|
|
|
N additional arguments after the 2nd filename in the pair_coeff
|
|
|
|
|
command, where N is the number of LAMMPS atom types:
|
|
|
|
|
</P>
|
|
|
|
|
<UL><LI>MEAM library file
|
|
|
|
|
<LI>Elem1, Elem2, ...
|
|
|
|
|
<LI>MEAM parameter file
|
|
|
|
|
<LI>N element names = mapping of MEAM elements to atom types
|
|
|
|
|
</UL>
|
|
|
|
|
<P>As an example, the potentials/library.meam file has generic MEAM
|
|
|
|
|
settings for a variety of elements. The potentials/sic.meam file has
|
|
|
|
|
specific parameter settings for a Si and C alloy system. If your
|
|
|
|
|
LAMMPS simulation has 4 atoms types and you want the 1st 3 to be Si,
|
|
|
|
|
and the 4th to be C, you would use the following pair_coeff command:
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>pair_coeff * * library.meam Si C sic.meam Si Si Si C
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>The 1st 2 arguments must be * * so as to span all LAMMPS atom types.
|
|
|
|
|
The two filenames are for the library and parameter file respectively.
|
|
|
|
|
The Si and C arguments (between the file names) are the two elements
|
|
|
|
|
for which info will be extracted from the library file. The first
|
|
|
|
|
three trailing Si arguments map LAMMPS atom types 1,2,3 to the MEAM Si
|
|
|
|
|
element. The final C argument maps LAMMPS atom type 4 to the MEAM C
|
|
|
|
|
element.
|
|
|
|
|
</P>
|
|
|
|
|
<P>If the 2nd filename is specified as NULL, no parameter file is read,
|
|
|
|
|
which simply means the generic parameters in the library file are
|
|
|
|
|
used. Use of the NULL specification for the parameter file is
|
|
|
|
|
discouraged for systems with more than a single element type
|
|
|
|
|
(e.g. alloys), since the parameter file is expected to set element
|
|
|
|
|
interaction terms that are not captured by the information in the
|
|
|
|
|
library file.
|
|
|
|
|
</P>
|
|
|
|
|
<P>If a mapping value is specified as NULL, the mapping is not performed.
|
|
|
|
|
This can be used when a <I>meam</I> potential is used as part of the
|
|
|
|
|
<I>hybrid</I> pair style. The NULL values are placeholders for atom types
|
|
|
|
|
that will be used with other potentials.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The MEAM library file provided with LAMMPS has the name
|
|
|
|
|
potentials/library.meam. It is the "meamf" file used by other MD
|
|
|
|
|
codes. Aside from blank and comment lines (start with #) which can
|
|
|
|
|
appear anywhere, it is formatted as a series of entries, each of which
|
|
|
|
|
has 19 parameters and can span multiple lines:
|
|
|
|
|
</P>
|
|
|
|
|
<P>elt, lat, z, ielement, atwt, alpha, b0, b1, b2, b3, alat, esub, asub,
|
|
|
|
|
t0, t1, t2, t3, rozero, ibar
|
|
|
|
|
</P>
|
|
|
|
|
<P>The "elt" and "lat" parameters are text strings, such as elt = Si or
|
|
|
|
|
Cu and lat = dia or fcc. Because the library file is used by Fortran
|
|
|
|
|
MD codes, these strings may be enclosed in single quotes, but this is
|
|
|
|
|
not required. The other numeric parameters match values in the
|
|
|
|
|
formulas above. The value of the "elt" string is what is used in the
|
|
|
|
|
pair_coeff command to identify which settings from the library file
|
|
|
|
|
you wish to read in. There can be multiple entries in the library
|
|
|
|
|
file with the same "elt" value; LAMMPS reads the 1st matching entry it
|
|
|
|
|
finds and ignores the rest.
|
|
|
|
|
</P>
|
|
|
|
|
<P>If used, the MEAM parameter file contains settings that override or
|
|
|
|
|
complement the library file settings. Examples of such parameter
|
|
|
|
|
files are in the potentials directory with a ".meam" suffix. Their
|
|
|
|
|
format is the same as is read by other Fortran MD codes. Aside from
|
|
|
|
|
blank and comment lines (start with #) which can appear anywhere, each
|
|
|
|
|
line has one of the following forms. Each line can also have a
|
|
|
|
|
trailing comment (starting with #) which is ignored.
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>keyword = value
|
|
|
|
|
keyword(I) = value
|
|
|
|
|
keyword(I,J) = value
|
|
|
|
|
keyword(I,J,K) = value
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>The recognized keywords are as follows:
|
|
|
|
|
</P>
|
|
|
|
|
<P>Ec, alpha, rho0, delta, lattce, attrac, repuls, nn2, Cmin, Cmax, rc, delr,
|
|
|
|
|
augt1, gsmooth_factor, re
|
|
|
|
|
</P>
|
|
|
|
|
<P>where
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>rc = cutoff radius for cutoff function; default = 4.0
|
|
|
|
|
delr = length of smoothing distance for cutoff function; default = 0.1
|
|
|
|
|
rho0(I) = relative density for element I (overwrites value
|
|
|
|
|
read from meamf file)
|
|
|
|
|
Ec(I,J) = cohesive energy of reference structure for I-J mixture
|
|
|
|
|
delta(I,J) = heat of formation for I-J alloy; if Ec_IJ is input as
|
2007-06-20 20:56:17 +08:00
|
|
|
zero, then LAMMPS sets Ec_IJ = (Ec_II + Ec_JJ)/2 - delta_IJ
|
2007-01-30 07:28:45 +08:00
|
|
|
alpha(I,J) = alpha parameter for pair potential between I and J (can
|
|
|
|
|
be computed from bulk modulus of reference structure
|
|
|
|
|
re(I,J) = equilibrium distance between I and J in the reference
|
|
|
|
|
structure
|
|
|
|
|
Cmax(I,J,K) = Cmax screening parameter when I-J pair is screened
|
|
|
|
|
by K (I<=J); default = 2.8
|
|
|
|
|
Cmin(I,J,K) = Cmin screening parameter when I-J pair is screened
|
|
|
|
|
by K (I<=J); default = 2.0
|
|
|
|
|
lattce(I,J) = lattice structure of I-J reference structure:
|
|
|
|
|
dia = diamond (interlaced fcc for alloy)
|
|
|
|
|
fcc = face centered cubic
|
|
|
|
|
bcc = body centered cubic
|
|
|
|
|
dim = dimer
|
2008-07-17 22:20:35 +08:00
|
|
|
b1 = rock salt (NaCl structure)
|
2007-01-30 07:28:45 +08:00
|
|
|
gsmooth_factor = factor determining the length of the G-function smoothing
|
|
|
|
|
region; only significant for ibar=0 or ibar=4.
|
|
|
|
|
99.0 = short smoothing region, sharp step
|
|
|
|
|
0.5 = long smoothing region, smooth step
|
|
|
|
|
default = 99.0
|
|
|
|
|
augt1 = integer flag for whether to augment t1 parameter by
|
|
|
|
|
3/5*t3 to account for old vs. new meam formulations;
|
|
|
|
|
0 = don't augment t1
|
|
|
|
|
1 = augment t1
|
|
|
|
|
default = 1
|
|
|
|
|
</PRE>
|
2007-06-20 20:56:17 +08:00
|
|
|
<P>Rc, delr, re are in distance units (Angstroms in the case of metal
|
|
|
|
|
units). Ec and delta are in energy units (eV in the case of metal
|
|
|
|
|
units).
|
|
|
|
|
</P>
|
2007-01-30 07:28:45 +08:00
|
|
|
<P>Each keyword represents a quantity which is either a scalar, vector,
|
|
|
|
|
2d array, or 3d array and must be specified with the correct
|
|
|
|
|
corresponding array syntax. The indices I,J,K each run from 1 to N
|
|
|
|
|
where N is the number of MEAM elements being used.
|
|
|
|
|
</P>
|
|
|
|
|
<P>Thus these lines
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>rho0(2) = 2.25
|
|
|
|
|
alpha(1,2) = 4.37
|
|
|
|
|
</PRE>
|
2007-02-10 05:40:32 +08:00
|
|
|
<P>set rho0 for the 2nd element to the value 2.25 and set alpha for the
|
|
|
|
|
alloy interaction between elements 1 and 2 to 4.37.
|
2007-01-30 07:28:45 +08:00
|
|
|
</P>
|
|
|
|
|
<HR>
|
|
|
|
|
|
2008-01-22 02:12:34 +08:00
|
|
|
<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
|
|
|
|
<P>For atom type pairs I,J and I != J, where types I and J correspond to
|
|
|
|
|
two different element types, mixing is performed by LAMMPS with
|
|
|
|
|
user-specifiable parameters as described above. You never need to
|
|
|
|
|
specify a pair_coeff command with I != J arguments for this style.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
|
|
|
|
|
shift, table, and tail options.
|
|
|
|
|
</P>
|
|
|
|
|
<P>This pair style does not write its information to <A HREF = "restart.html">binary restart
|
|
|
|
|
files</A>, since it is stored in potential files. Thus, you
|
|
|
|
|
need to re-specify the pair_style and pair_coeff commands in an input
|
|
|
|
|
script that reads a restart file.
|
|
|
|
|
</P>
|
2007-10-04 08:21:14 +08:00
|
|
|
<P>This pair style can only be used via the <I>pair</I> keyword of the
|
|
|
|
|
<A HREF = "run_style.html">run_style respa</A> command. It does not support the
|
2007-10-12 07:09:49 +08:00
|
|
|
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
|
2007-10-04 08:21:14 +08:00
|
|
|
</P>
|
2007-06-26 08:03:39 +08:00
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<P><B>Restrictions:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>This style is part of the "meam" package. It is only enabled if
|
|
|
|
|
LAMMPS was built with that package, which also requires the MEAM
|
|
|
|
|
library be built and linked with LAMMPS. See the <A HREF = "Section_start.html#2_3">Making
|
|
|
|
|
LAMMPS</A> section for more info.
|
2007-01-30 07:28:45 +08:00
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B>
|
|
|
|
|
</P>
|
2007-02-10 05:40:32 +08:00
|
|
|
<P><A HREF = "pair_coeff.html">pair_coeff</A>, <A HREF = "pair_eam.html">pair_style eam</A>
|
2007-01-30 07:28:45 +08:00
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<A NAME = "Baskes"></A>
|
|
|
|
|
|
|
|
|
|
<P><B>(Baskes)</B> Baskes, Phys Rev B, 46, 2727-2742 (1992).
|
|
|
|
|
</P>
|
|
|
|
|
<A NAME = "Gullet"></A>
|
|
|
|
|
|
|
|
|
|
<P><B>(Gullet)</B> Gullet, Wagner, Slepoy, SANDIA Report 2003-8782 (2003).
|
|
|
|
|
This report may be accessed on-line via <A HREF = "http://www.prod.sandia.gov/cgi-bin/techlib/access-control.pl/2003/038782.pdf">this link</A>.
|
|
|
|
|
</P>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
</HTML>
|
