"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c :link(lws,http://lammps.sandia.gov) :link(ld,Manual.html) :link(lc,Section_commands.html#comm) :line pair_style eam command :h3 pair_style eam/alloy command :h3 pair_style eam/fs command :h3 [Syntax:] pair_style style :pre style = {eam} or {eam/alloy} or {eam/fs} :ul [Examples:] pair_style eam pair_coeff * * cuu3 pair_coeff 1*3 1*3 niu3 :pre pair_style eam/alloy pair_coeff * * nialhjea 1 2 1 1 :pre pair_style eam/fs pair_coeff * * nial.fs 1 2 1 1 :pre [Description:] Style {eam} computes pairwise interactions for metals and metal alloys using embedded-atom method (EAM) potentials "(Daw)"_#Daw. The total energy Ei of an atom I is given by :c,image(Eqs/pair_eam.jpg) where F is the embedding energy which is a function of the atomic electron density rho, phi is a pair potential interaction, and alpha and beta are the element types of atoms I and J. The multi-body nature of the EAM potential is a result of the embedding energy term. Both summations in the formula are over all neighbors J of atom I within the cutoff distance. The cutoff distance and the tabulated values of the functionals F, rho, and phi are listed in one or more files which are specified by the "pair_coeff"_pair_coeff.html command. These are ASCII text files in a DYNAMO-style format which is described in the documentation for the "pair_coeff"_pair_coeff.html command. DYNAMO is a serial MD code Several DYNAMO potential files for different metals are included in the "potentials" directory of the LAMMPS distribution. IMPORTANT NOTE: The {eam} style reads single-element EAM potentials in the DYNAMO {funcfl} format. Either single element or alloy systems can be modeled with {funcfl} files and style {eam}. For the alloy case LAMMPS mixes the single-element potentials to produce alloy potentials the same way that DYNAMO does. Alternatively, DYNAMO {setfl} files can be used by LAMMPS to model alloy systems by invoking the {eam/alloy} style as described below. {Setfl} files require no mixing since they specify alloy interactions explicitly. For style {eam}, potential values are read from a file that is in the DYNAMO single-element {funcfl} format. If the DYNAMO file was created by a Fortran program, it cannot have "D" values in it for exponents. C only recognizes "e" or "E" for scientific notation. Note that unlike for other potentials, you do not set cutoffs for EAM potentials in the pair_style or pair_coeff command; they are specified in the EAM potential files. For style {eam} you must assign a potential file to each I,I pair of atom types by using a single pair_coeff argument: filename :ul Thus the following command pair_coeff *2 1*2 cuu3 :pre will read the cuu3 potential file and use the tabulated Cu values for F, phi, rho that it contains for type pairs 1,1 and 2,2 (type pairs 1,2 and 2,1 are ignored). In effect, this makes atom types 1 and 2 in LAMMPS be Cu atoms. Different single-element files can be assigned to different atom types to model an alloy system. The mixing to create alloy potentials for type pairs with I != J is done automatically the same way that the serial DYANMO code originally did it; you do not need to specify coefficients for these type pairs. There are several {funcl} files in the {potentials} directory of the LAMMPS distribution, with the suffix ".eam". A DYNAMO single-element {funcfl} file is formatted as follows: line 1: comment (ignored) line 2: atomic number, mass, lattice constant, lattice type (e.g. FCC) line 3: Nrho, drho, Nr, dr, cutoff :ul On line 2, all values but the mass are ignored by LAMMPS. The mass is in atomic mass units which is converted by LAMMPS to the appropriate internal mass "units"_units.html. On line 3, Nrho and Nr are the number of tabulated values in the subsequent arrays, drho and dr are the spacing in density and distance space for the values in those arrays, and the specified cutoff becomes the pairwise cutoff used by LAMMPS for the potential. The units of dr are Angstroms; I'm not sure of the units for drho - some measure of electron density. Following the 3 header lines are 3 arrays of tabulated values: embedding function F (Nrho values) pair potential function phi (Nr values) density function rho (Nr values) :ul The values for each array can be listed as multiple values per line, so long as each array starts on a new line. The individual values are (for example) phi(r) for r = 0,dr,2*dr, ... (Nr-1)*dr. :line Style {eam/alloy} computes pairwise interactions using the same formula as style {eam}. However the associated "pair_coeff"_pair_coeff.html command reads a DYNAMO {setfl} file instead of a {funcfl} file. {Setfl} files can be used to model a single-element or alloy system. In the alloy case, as explained above, {setfl} files contain explicit tabulated values for alloy interactions. Thus they allow more generality than {funcfl} files for modeling alloys. For style {eam/alloy}, potential values are read from a file that is in the DYNAMO multi-element {setfl} format. If the DYNAMO file was created by a Fortran program, it cannot have "D" values in it for exponents. C only recognizes "e" or "E" for scientific notation. Only one pair_coeff command can be used (one file). DYNAMO {setfl} files contain information for M elements. These are mapped to LAMMPS atom types by specifying N additional arguments after the filename, where N is the number of LAMMPS atom types: filename N values from 0 to M = mapping of {setfl} elements to atom types :ul As an example, the nialhjea {setfl} file has tabulated EAM values for 3 elements and their alloy interactions: Ni, Al, and H. If your LAMMPS simulation has 4 atoms types and you want the 1st 3 to be Ni, and the 4th to be Al, you would use the following pair_coeff command: pair_coeff * * nialhjea 1 1 1 2 :pre The 1st 2 arguments must be * * so as to span all LAMMPS atom types. The first three "1" values map LAMMPS atom types 1,2,3 to the 1st element (Ni) in the {setfl} file. The final "2" value maps LAMMPS atom type 4 to the 2nd element = Al. If a mapping value is "0", the mapping is not performed. This can be used when an {eam/alloy} potential is used as part of the {hybrid} pair style. The 0 values are used as placeholders for atom types that will be used with other potentials. {Setfl} files in the {potentials} directory of the LAMMPS distribution have a ".eam.alloy" suffix. A DYNAMO multi-element {setfl} file is formatted as follows: lines 1,2,3 = comments (ignored) line 4: Nelements = # of elements in the file line 5: Nrho, drho, Nr, dr, cutoff :ul The meaning of the values in line 5 is the same as for the {funcfl} file described above. Note that the cutoff is a global value, valid for all pairwise interactions for all element pairings. Following the 5 header lines are Nelements sections, one for each element, each with the following format: line 1 = atomic number, mass, lattice constant, lattice type (e.g. FCC) embedding function F (Nrho values) density function rho (Nr values) :ul As with the {funcfl} files, only the mass is used by LAMMPS from the 1st line. The F and rho arrays are unique to a single element and are formatted the same as in a {funcfl} file. Following the Nelements sections, values for the pair potential phi arrays are listed for all i,j element pairs in the same format as other arrays. Since these interactions are symmetric (i,j = j,i) only phi arrays with i >= j are listed, in the following order: i,j = (1,1), (2,1), (2,2), (3,1), (3,2), (3,3), (4,1), ..., (Nelements, Nelements). The tabulated values for each phi function are listed in {setfl} files as r*phi, rather than as phi (in {funcfl} files). :line Style {eam/fs} computes pairwise interactions for metals and metal alloys using a generalized form of EAM potentials due to Finnis and Sinclair "(Finnis)"_#Finnis. The total energy Ei of an atom I is given by :c,image(Eqs/pair_eam_fs.jpg) This has the same form as the EAM formula above, except that rho is now a functional specific to the atomic types of both atoms I and J, so that different elements can contribute differently to the total electron density at an atomic site depending on the identity of the element at that atomic site. The associated "pair_coeff"_pair_coeff.html command for style {eam/fs} reads a DYNAMO {setfl} file that has been extended to include additional rho_alpha_beta arrays of tabulated values. The details are given in the "pair_coeff"_pair_coeff.html documentation. A discussion of how FS EAM differs from conventional EAM alloy potentials is given in "(Ackland1)"_#Ackland1. An example of such a potential is the same author's Fe-P FS potential "(Ackland2)"_#Ackland2. Note that while FS potentials always specify the embedding energy with a square root dependence on the total density, the implementation in LAMMPS does not require that; the user can tabulate any functional form he desires in the FS potential files. For style {eam/fs}, the form of the pair_coeff command is exactly the same as for style {eam/alloy}, e.g. pair_coeff * * filename 1 1 1 2 :pre where there are N additional arguments after the filename, where N is the number of LAMMPS atom types. The N values determine the mapping of LAMMPS atom types to EAM elements in the file, as described above for style {eam/alloy}. As with {eam/alloy}, if a mapping value is "0", the mapping is not performed. This can be used when an {eam/fs} potential is used as part of the {hybrid} pair style. The 0 values are used as placeholders for atom types that will be used with other potentials. FS EAM files include more information than the DYNAMO {setfl} format files read by {eam/alloy}, so that the i,j density functionals for all pairs of elements are included as needed by the Finnis/Sinclair formulation of the EAM. FS EAM files in the {potentials} directory of the LAMMPS distribution have a ".eam.fs" suffix. Ther are formatted as follows: lines 1,2,3 = comments (ignored) line 4: Nelements = # of elements in the file line 5: Nrho, drho, Nr, dr, cutoff :ul The 5-line header section is identical to an EAM {setfl} file. Following the header are Nelements sections, one for each element I, each with the following format: line 1 = atomic number, mass, lattice constant, lattice type (e.g. FCC) embedding function F (Nrho values) density function rho for element I at element 1 (Nr values) density function rho for element I at element 2 ... density function rho for element I at element Nelement :ul Following the Nelements sections, values for the pair potential phi arrays are listed in the same manner (r*phi) as in EAM {setfl} files. Note that the rho arrays in Finnis/Sinclair can be asymmetric (i,j != j,i) so there are Nelements^2 of them listed in the file. But the phi arrays are still symmetric, so only phi arrays for i >= j are listed. :line [Restrictions:] none [Related commands:] "pair_coeff"_pair_coeff.html [Default:] none :line :link(Ackland1) [(Ackland1)] Ackland, Condensed Matter (2005). :link(Ackland2) [(Ackland2)] Ackland, Mendelev, Srolovitz, Han and Barashev, Journal of Physics: Condensed Matter, 16, S2629 (2004). :link(Daw) [(Daw)] Daw, Baskes, Phys Rev Lett, 50, 1285 (1983). Daw, Baskes, Phys Rev B, 29, 6443 (1984). :link(Finnis) [(Finnis)] Finnis, Sinclair, Philosophical Magazine A, 50, 45 (1984).