\(\renewcommand{\AA}{\text{Å}}\)

bond_style quartic/exp command

Accelerator Variants: quartic/exp/kk

Syntax

bond_style quartic/exp

Examples

bond_style quartic/exp
bond_coeff 1 1.54 200.0 -100.0 50.0 0.0 1.0
bond_coeff 2 1.0 500.0 0.0 -200.0 1000.0 0.3

Description

Added in version TBD.

The quartic/exp bond style uses the potential

\[E = k_2 (r - r_0)^2 + k_3 (r - r_0)^3 + k_4 (r - r_0)^4 + A \exp\left(-\frac{r}{B}\right)\]

where \(r_0\) is the equilibrium bond distance. The first three terms form a quartic polynomial in the bond displacement \((r - r_0)\) that can model anharmonic stretching. The optional exponential term (\(A \exp(-r/B)\)) adds a repulsive or attractive wall at short range. Setting \(A = 0\) disables the exponential term entirely.

The following coefficients must be defined for each bond type via the bond_coeff command as in the examples above, or in the data file or restart files read by the read_data or read_restart commands:

  • \(r_0\) (distance)

  • \(k_2\) (energy/distance^2)

  • \(k_3\) (energy/distance^3)

  • \(k_4\) (energy/distance^4)

  • \(A\) (energy)

  • \(B\) (distance, must be non-zero if \(A \neq 0\))

Note that the \(k_2\) coefficient plays the role of the spring constant. The \(k_3\) and \(k_4\) coefficients introduce anharmonicity. Setting \(k_3 = k_4 = 0\) and \(A = 0\) reduces this style to bond_style harmonic with \(K = k_2\) (the factor of 1/2 is not included in \(k_2\) here).

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 bond style can only be used if LAMMPS was built with the EXTRA-MOLECULE package. See the Build package page for more info.

The parameter \(B\) must be non-zero whenever \(A \neq 0\).

Default

none