\(\renewcommand{\AA}{\text{Å}}\)
improper_style inversion/harmonic command
Accelerator Variants: inversion/harmonic/kk, inversion/harmonic/omp
Syntax
improper_style inversion/harmonic
Examples
improper_style inversion/harmonic
improper_coeff 1 18.776340 0.000000
Description
The inversion/harmonic improper style follows the Wilson-Decius out-of-plane angle definition and uses an harmonic potential:
where \(K\) is the force constant and \(\omega\) is the angle evaluated for all three axis-plane combinations centered around the atom I. For the IL axis and the IJK plane \(\omega\) looks as follows:
Note that the inversion/harmonic angle term evaluation differs to the improper_umbrella due to the cyclic evaluation of all possible angles \(\omega\).
The following coefficients must be defined for each improper type via the improper_coeff command as in the example above, or in the data file or restart files read by the read_data or read_restart commands:
\(K\) (energy)
\(\omega_0\) (degrees)
If \(\omega_0 = 0\) the potential term has a single minimum for the planar structure. Otherwise it has two minima at +/- \(\omega_0\), with a barrier in between.
Symmetry convention
For the inversion/harmonic improper style, the first atom in the quadruplet is the atom of symmetry; all other atoms are considered interchangeable. This convention is relevant for operations that require knowledge of how atoms are ordered, such as automatic assignment of new improper types by fix bond/react.
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 Accelerator packages 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, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package 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 Accelerator packages page for more instructions on how to use the accelerated styles effectively.
Restrictions
This improper style can only be used if LAMMPS was built with the MOFFF package. See the Build package doc page for more info.
Default
none