compute ID group-ID coord/atom cutoff type1 type2 ...
compute 1 all coord/atom 2.0 compute 1 all coord/atom 6.0 1 2 compute 1 all coord/atom 6.0 2*4 5*8 *
Define a computation that calculates one or more coordination numbers for each atom in a group.
A coordination number is defined as the number of neighbor atoms with specified atom type(s) that are within the specified cutoff distance from the central atom. Atoms not in the group are included in a coordination number of atoms in the group.
The typeN keywords allow you to specify which atom types contribute to each coordination number. One coordination number is computed for each of the typeN keywords listed. If no typeN keywords are listed, a single coordination number is calculated, which includes atoms of all types (same as the "*" format, see below).
The typeN keywords can be specified in one of two ways. An explicit numeric value can be used, as in the 2nd example above. Or a wild-card asterisk can be used to specify a range of atom types. This takes the form "*" or "*n" or "n*" or "m*n". If N = the number of atom types, then an asterisk with no numeric values means all types from 1 to N. A leading asterisk means all types from 1 to n (inclusive). A trailing asterisk means all types from n to N (inclusive). A middle asterisk means all types from m to n (inclusive).
The value of all coordination numbers will be 0.0 for atoms not in the specified compute group.
The neighbor list needed to compute this quantity is constructed each time the calculation is performed (i.e. each time a snapshot of atoms is dumped). Thus it can be inefficient to compute/dump this quantity too frequently.
If single type1 keyword is specified (or if none are specified), this compute calculates a per-atom vector. If multiple typeN keywords are specified, this compute calculates a per-atom array, with N columns. These values can be accessed by any command that uses per-atom values from a compute as input. See Section_howto 15 for an overview of LAMMPS output options.
The per-atom vector or array values will be a number >= 0.0, as explained above.