kim-api  2.1.4-git+v2.1.3-git-3-g4c859c7f.GNU
An Application Programming Interface (API) for the Knowledgebase of Interatomic Models (KIM).
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26 # Ellad B. Tadmor
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28 
29 Spring-modified Lennard-Jones (SLJ) pair potential model for Ar.
30 
31 V = 0.5 \sum_i \sum_j eps_i eps_j 4 [ (sig/r_ij)^12 - (sig/r_ij)^6 ] (1)
32 
33 where
34  eps_i = 0.5 \sum_k spring (r_ik)^2 (2)
35 
36 The potential parameters are `sig` and the spring constant `sig`.
37 
38 This potential uses two cutoffs and requires neighbors of padding
39 atoms for the summ in (2).
40 
41 The loops in (2) are over all atoms for which r_ik < cutoff1
42 
43 The loops in (1) are over all atoms for which r_ij < cutoff2
44 
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
49 only.
50 
51 The equilibrium spacing for the fcc structure predicted by the SLJ potential is
52 
53 a0 = 2^(1/3)/sqrt(3) * (94297/491)^(1/6) sig = 1.74724 sig
54 
55 The first, second and third neighbor distances in fcc are then:
56 
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
60 
61 The parameters `sig` and `spring` are selected to reproduce the experimental
62 properties of fcc argon:
63 
64 a0 = 5.26 A
65 E_c = 0.0104 eV