4 # The contents of this file are subject to the terms of the Common Development

5 # and Distribution License Version 1.0 (the "License").

7 # You can obtain a copy of the license at

8 # http://www.opensource.org/licenses/CDDL-1.0. See the License for the

9 # specific language governing permissions and limitations under the License.

11 # When distributing Covered Code, include this CDDL HEADER in each file and

12 # include the License file in a prominent location with the name LICENSE.CDDL.

13 # If applicable, add the following below this CDDL HEADER, with the fields

14 # enclosed by brackets "[]" replaced with your own identifying information:

16 # Portions Copyright (c) [yyyy] [name of copyright owner]. All rights reserved.

22 # Copyright (c) 2013--2019, Regents of the University of Minnesota.

23 # All rights reserved.

29 Spring-modified Lennard-Jones (SLJ) pair potential model for Ar.

31 V = 0.5 \sum_i \sum_j eps_i eps_j 4 [ (sig/r_ij)^12 - (sig/r_ij)^6 ] (1)

34 eps_i = 0.5 \sum_k spring (r_ik)^2 (2)

36 The potential parameters are `sig` and the spring constant `sig`.

38 This potential uses two cutoffs and requires neighbors of padding

39 atoms for the summ in (2).

41 The loops in (2) are over all atoms for which r_ik < cutoff1

43 The loops in (1) are over all atoms for which r_ij < cutoff2

45 For the Ar parameterization, cutoff1 is set so that only nearest

46 neighbors contribute in the equilibrium 0K fcc structure, and

47 cutoff2 is set to include the third neighbor distance. The potential

48 is discontinuous at both cutoffs. It is designed for testing purposes

51 The equilibrium spacing for the fcc structure predicted by the SLJ potential is

53 a0 = 2^(1/3)/sqrt(3) * (94297/491)^(1/6) sig = 1.74724 sig

55 The first, second and third neighbor distances in fcc are then:

57 r_NN1 = a0/sqrt(2) = 1.235 sig

58 r_NN2 = a0 = 1.747 sig

59 r_NN3 = a0*sqrt(3/2) = 2.140 sig

61 The parameters `sig` and `spring` are selected to reproduce the experimental

62 properties of fcc argon: