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# Copyright (c) 2012, Regents of the University of Minnesota.  All rights reserved.
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# Contributors:
#    Ryan S. Elliott
#    Ellad B. Tadmor
#    Valeriu Smirichinski
#    Amit Singh
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This directory (Three_Body_Stillinger_Weber__MD_335816936951_001) contains Stillinger-Weber potential
Model driver written in C.


/*******************************************************************************

* For three-body potential any potential energy function for N-particle system can be written in the
* following form of two-body and three-body terms:
     F(1, 2, ...., N)   = sum_{i; 1 <= i < j <= N} phi_two(r; r = r_ij)
                          + sum_{i; 1 <= i \neq j < k <= N} phi_three(r_ij, r_ik, r_jk);

* For Stillinger-Weber, two-body term phi_two is

     phi_two(r) = epsilon * f_2(r_cap; r_cap = r/sigma); where f_2 is

     f_2(r_cap) = A * ( B*r_cap^(-p) - r_cap^-q ) * exp(1/(r_cap - a)); when  r_cap <  a
                = 0   when r_cap >= a

* and three-body term phi_three is

     phi_three(r_ij, r_ik, r_jk) = epsilon * f_3(r1_cap, r2_cap, r3_cap); where

     r1_cap = r_ij/sigma, r2_cap = r_ik/sigma, r3_cap = r_jk/sigma,      and

     f_3(r1_cap, r2_cap, r3_cap) = lambda * (exp(gamma((1/(r1_cap - a)) + (1/(r2_cap - a))))) * (costheta_jik - costheta_0)^2;  when r1_cap < a && r2_cap < a
                                 = 0;                                                                                           otherwise

     costheta_jik = (r_ij^2 + r_ik^2 - r_jk^2) / (2*r_ij*r_ik).

*******************************************************************************/

For Silicon:
------------------------------------------------------------
| A = 7.049556277, B = 0.6022245584, p = 4, q = 0,          |
| a = 1.80, lambda = 21.0, gamma = 1.2,                     |
| sigma = 2.0951, epsilon = 2.315 ev (for E_coh = 4.63 ev), |
| costheta_0 = -1/3                                         |
-------------------------------------------------------------

References:

1. F. H. Stillinger and T. A. Weber, "Computer simulation of local order in condensed phases of silicon", Phys. Rev. B, vol. 31, 5262-5271, 1985

2. Ellad B. Tadmor and Ronald E. Miller, Modeling Materials: Continuum, Atomistic and Multiscale Techniques, Cambridge University Press, 2011

It complies with the KIM API interface standard, using two neihgbor handling methods,
NEIGH_PURE_F and NEIGH_RVEC_F and iterator or locator mode. It publishes its parameters
and supports optional computation of `energy', 'forces', 'particleEnergy', 'process_dEdr',
and 'process_dE2dr2'. Its initializaton routine takes a KIM API object pointer and
a pointer to a string that contains all parameters which define a KIM Model
based on this KIM Model Driver.


To create a KIM Model from this Model Driver, a parameter file is required.
This file must have the follwing format:
   Line 1: A
   Line 2: B
   Line 3: p
   Line 4: q
   Line 5: a
   Line 6: lambda
   Line 7: gamma
   Line 8: sigma in Angstrom
   Line 9: epsilon in ev
   Line 10: costheta_0
Any additional lines will be silently ignored.


The following files are in this directory:

LICENSE.CDDL
     The Common Development and Distribution License (CDDL) Version 1.0 file

Makefile
    makefile to compile and build executables with GNU or Intel compilers

README
    This file

Three_Body_Stillinger_Weber.c
    C file that contains the implementation of the 3-body Stillinger-Weber potential
    Model Driver

Three_Body_Stillinger_Weber.kim.tpl
    Template KIM descriptor file containing all variables and methods that are
    exposed by the driver through the KIM API interface.  This file will be
    used (by the make system) to generate a KIM descriptor file for each KIM
    Model based on this Model Driver.