kim-api  2.3.0+v2.3.0.GNU.GNU.
An Application Programming Interface (API) for the Knowledgebase of Interatomic Models (KIM).
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1 #
2 # KIM-API: An API for interatomic models
3 # Copyright (c) 2013--2022, Regents of the University of Minnesota.
4 # All rights reserved.
5 #
6 # Contributors:
7 # Ellad B. Tadmor
8 #
9 # SPDX-License-Identifier: LGPL-2.1-or-later
10 #
11 # This library is free software; you can redistribute it and/or
12 # modify it under the terms of the GNU Lesser General Public
13 # License as published by the Free Software Foundation; either
14 # version 2.1 of the License, or (at your option) any later version.
15 #
16 # This library is distributed in the hope that it will be useful,
17 # but WITHOUT ANY WARRANTY; without even the implied warranty of
18 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 # Lesser General Public License for more details.
20 #
21 # You should have received a copy of the GNU Lesser General Public License
22 # along with this library; if not, write to the Free Software Foundation,
23 # Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
24 #
25 
26 
27 Spring-modified Lennard-Jones (SLJ) pair potential model for Ar.
28 
29 V = 0.5 \sum_i \sum_j eps_i eps_j 4 [ (sig/r_ij)^12 - (sig/r_ij)^6 ] (1)
30 
31 where
32  eps_i = 0.5 \sum_k spring (r_ik)^2 (2)
33 
34 The potential parameters are `sig` and the spring constant `sig`.
35 
36 This potential uses two cutoffs and requires neighbors of padding
37 atoms for the summ in (2).
38 
39 The loops in (2) are over all atoms for which r_ik < cutoff1
40 
41 The loops in (1) are over all atoms for which r_ij < cutoff2
42 
43 For the Ar parameterization, cutoff1 is set so that only nearest
44 neighbors contribute in the equilibrium 0K fcc structure, and
45 cutoff2 is set to include the third neighbor distance. The potential
46 is discontinuous at both cutoffs. It is designed for testing purposes
47 only.
48 
49 The equilibrium spacing for the fcc structure predicted by the SLJ potential is
50 
51 a0 = 2^(1/3)/sqrt(3) * (94297/491)^(1/6) sig = 1.74724 sig
52 
53 The first, second and third neighbor distances in fcc are then:
54 
55 r_NN1 = a0/sqrt(2) = 1.235 sig
56 r_NN2 = a0 = 1.747 sig
57 r_NN3 = a0*sqrt(3/2) = 2.140 sig
58 
59 The parameters `sig` and `spring` are selected to reproduce the experimental
60 properties of fcc argon:
61 
62 a0 = 5.26 A
63 E_c = 0.0104 eV