angle_style cosine/periodic command
angle_style cosine/periodic/omp command
angle_style cosine/periodic angle_coeff * 75.0 1 6
The cosine/periodic angle style uses the following potential, which is commonly used in the DREIDING force field, particularly for organometallic systems where n = 4 might be used for an octahedral complex and n = 3 might be used for a trigonal center:
where C, B and n are coefficients defined for each angle type.
See (Mayo) for a description of the DREIDING force field
The following coefficients must be defined for each angle type via the angle_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:
B = 1 or -1
n = 1, 2, 3, 4, 5 or 6 for periodicity
Note that the prefactor C is specified and not the overall force constant K = C / n^2. When B = 1, it leads to a minimum for the linear geometry. When B = -1, it leads to a maximum for the linear geometry.
Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Speed packages doc page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.
These accelerated styles are part of the GPU, USER-INTEL, KOKKOS, USER-OMP and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package doc page for more info.
You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.
See the Speed packages doc page for more instructions on how to use the accelerated styles effectively.
This angle style can only be used if LAMMPS was built with the MOLECULE package. See the Build package doc page for more info.