Syntax:
-compute ID group-ID group/group group2-ID +compute ID group-ID group/group group2-ID keyword value ...-
pair value = yes or no + kspace value = yes or no ++
Examples:
compute 1 lower group/group upper +compute 1 lower group/group upper kspace yes compute mine fluid group/group wall
Description:
Define a computation that calculates the total energy and force interaction between two groups of atoms: the compute group and the -specified group2. The two groups can be the same. The interaction -energy is defined as the pairwise energy between all pairs of atoms -where one atom in the pair is in the first group and the other is in -the second group. Likewise, the interaction force calculated by this -compute is the force on the compute group atoms due to pairwise +specified group2. The two groups can be the same. +
+If the pair keyword is set to yes, which is the default, then the +the interaction energy will include a pair component which is defined +as the pairwise energy between all pairs of atoms where one atom in +the pair is in the first group and the other is in the second group. +Likewise, the interaction force calculated by this compute will +include the force on the compute group atoms due to pairwise interactions with atoms in the specified group2.
-The energy and force are calculated by looping over a neighbor list of -pairwise interactions. Thus it can be inefficient to compute this -quantity too frequently. +
If the kspace keyword is set to yes, which is not the default, and +if a kspace_style is defined, then the the +interaction energy will include a Kspace component which is the +long-range Coulombic energy between all the atoms in the first group +and all the atoms in the 2nd group. group. Likewise, the interaction +force calculated by this compute will include the force on the compute +group atoms due to long-range Coulombic interactions with atoms in the +specified group2. +
+This compute does not calculate any bond or angle or dihedral or +improper interactions between atoms in the two groups. +
+The pairwise contributions to the group-group interactions are +calculated by looping over a neighbor list. The Kspace contribution +to the group-group interactions require essentially the same amount of +work (FFTs, Ewald summation) as computing long-range forces for the +entire system. Thus it can be costly to invoke this compute too +frequently. +
+If you desire a breakdown of the interactions into a pairwise and +Kspace component, simply invoke the compute twice with the appropriate +yes/no settings for the pair and kspace keywords. This is no more +costly than using a single compute with both keywords set to yes. +The individual contributions can be summed in a +variable if desired. +
+Thie document describes how the long-range +group-group calculations are performed.
Output info:
@@ -54,20 +96,20 @@ The vector values will be in force units.Restrictions:
-Only pairwise interactions, as defined by the -pair_style command, are included in this -calculation. Bond (angle, dihedral, etc) interactions between atoms -in the two groups are not included. Long-range interactions due to a -kspace_style command are also not included. Not -all pair potentials can be evaluated in a pairwise mode as required by -this compute. For example, 3-body potentials, such as -Tersoff and Stillinger-Weber cannot -be used. EAM potentials for metals only include the -pair potential portion of the EAM interaction, not the embedding -term. +
Not all pair styles can be evaluated in a pairwise mode as required by +this compute. For example, 3-body and other many-body potentials, +such as Tersoff and +Stillinger-Weber cannot be used. EAM +potentials only include the pair potential portion of the EAM +interaction when used by this compute, not the embedding term. +
+Not all Kspace styles support calculation of group/group interactions. +The ewald and pppm styles do.
Related commands: none
-Default: none +
Default: +
+The option defaults are pair = yes and kspace = no.