1 "LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
3 :link(lws,http://lammps.sandia.gov)
5 :link(lc,Section_commands.html#comm)
9 pair_style srp command :h3
13 pair_style srp cutoff btype dist keyword value ...
15 cutoff = global cutoff for SRP interactions (distance units) :ulb,l
16 btype = bond type to apply SRP interactions to (can be wildcard, see below) :l
17 distance = {min} or {mid} :l
18 zero or more keyword/value pairs may be appended :l
19 keyword = {exclude} :l
20 {bptype} value = atom type for bond particles
21 {exclude} value = {yes} or {no} :pre
26 pair_style hybrid dpd 1.0 1.0 12345 srp 0.8 1 mid exclude yes
27 pair_coeff 1 1 dpd 60.0 4.5 1.0
29 pair_coeff 2 2 srp 100.0 0.8 :pre
31 pair_style hybrid dpd 1.0 1.0 12345 srp 0.8 * min exclude yes
32 pair_coeff 1 1 dpd 60.0 50 1.0
34 pair_coeff 2 2 srp 40.0 :pre
36 pair_style hybrid srp 0.8 2 mid
39 pair_coeff 2 2 srp 100.0 0.8 :pre
43 Style {srp} computes a soft segmental repulsive potential (SRP) that
44 acts between pairs of bonds. This potential is useful for preventing
45 bonds from passing through one another when a soft non-bonded
46 potential acts between beads in, for example, DPD polymer chains. An
47 example input script that uses this command is provided in
50 Bonds of specified type {btype} interact with one another through a
51 bond-pairwise potential, such that the force on bond {i} due to bond
54 :c,image(Eqs/pair_srp1.jpg)
56 where {r} and {rij} are the distance and unit vector between the two
57 bonds. Note that {btype} can be specified as an asterisk "*", which
58 case the interaction is applied to all bond types. The {mid} option
59 computes {r} and {rij} from the midpoint distance between bonds. The
60 {min} option computes {r} and {rij} from the minimum distance between
61 bonds. The force acting on a bond is mapped onto the two bond atoms
62 according to the lever rule,
64 :c,image(Eqs/pair_srp2.jpg)
66 where {L} is the normalized distance from the atom to the point of
67 closest approach of bond {i} and {j}. The {mid} option takes {L} as
68 0.5 for each interaction as described in "(Sirk)"_#Sirk.
70 The following coefficients must be defined via the
71 "pair_coeff"_pair_coeff.html command as in the examples above, or in
72 the data file or restart file read by the "read_data"_read_data.html
73 or "read_restart"_read_restart.html commands:
76 {rc} (distance units) :ul
78 The last coefficient is optional. If not specified, the global cutoff
81 NOTE: Pair style srp considers each bond of type {btype} to be a
82 fictitious "particle" of type {bptype}, where {bptype} is either the
83 largest atom type in the system, or the type set by the {bptype} flag.
84 Any actual existing particles with this atom type will be deleted at
85 the beginning of a run. This means you must specify the number of
86 types in your system accordingly; usually to be one larger than what
87 would normally be the case, e.g. via the "create_box"_create_box.html
88 or by changing the header in your "data file"_read_data.html. The
89 ficitious "bond particles" are inserted at the beginning of the run,
90 and serve as placeholders that define the position of the bonds. This
91 allows neighbor lists to be constructed and pairwise interactions to
92 be computed in almost the same way as is done for actual particles.
93 Because bonds interact only with other bonds, "pair_style
94 hybrid"_pair_hybrid.html should be used to turn off interactions
95 between atom type {bptype} and all other types of atoms. An error
96 will be flagged if "pair_style hybrid"_pair_hybrid.html is not used.
98 The optional {exclude} keyword determines if forces are computed
99 between first neighbor (directly connected) bonds. For a setting of
100 {no}, first neighbor forces are computed; for {yes} they are not
101 computed. A setting of {no} cannot be used with the {min} option for
102 distance calculation because the minimum distance between directly
103 connected bonds is zero.
105 Pair style {srp} turns off normalization of thermodynamic properties
106 by particle number, as if the command "thermo_modify norm
107 no"_thermo_modify.html had been issued.
109 The pairwise energy associated with style {srp} is shifted to be zero
110 at the cutoff distance {rc}.
114 [Mixing, shift, table, tail correction, restart, rRESPA info]:
116 This pair styles does not support mixing.
118 This pair style does not support the "pair_modify"_pair_modify.html
119 shift option for the energy of the pair interaction. Note that as
120 discussed above, the energy term is already shifted to be 0.0 at the
121 cutoff distance {rc}.
123 The "pair_modify"_pair_modify.html table option is not relevant for
126 This pair style does not support the "pair_modify"_pair_modify.html
127 tail option for adding long-range tail corrections to energy and
130 This pair style writes global and per-atom information to "binary
131 restart files"_restart.html. Pair srp should be used with "pair_style
132 hybrid"_pair_hybrid.html, thus the pair_coeff commands need to be
133 specified in the input script when reading a restart file.
135 This pair style can only be used via the {pair} keyword of the
136 "run_style respa"_run_style.html command. It does not support the
137 {inner}, {middle}, {outer} keywords.
143 This pair style is part of the USER-MISC package. It is only enabled
144 if LAMMPS was built with that package. See the Making LAMMPS section
147 This pair style must be used with "pair_style
148 hybrid"_pair_hybrid.html.
150 This pair style requires the "newton"_newton.html command to be {on}
151 for non-bonded interactions.
155 "pair_style hybrid"_pair_hybrid.html, "pair_coeff"_pair_coeff.html,
156 "pair dpd"_pair_dpd.html
160 The default keyword value is exclude = yes.
165 [(Sirk)] Sirk TW, Sliozberg YR, Brennan JK, Lisal M, Andzelm JW, J
166 Chem Phys, 136 (13) 134903, 2012.