Coulomb (cutoff)¶

Description¶

The coul_cut_compute_force operator calculates the Coulomb pair potential with a simple real-space cutoff:

\[ E(r) = \frac{1}{4\pi \varepsilon_0 \varepsilon_r} \frac{q_i q_j}{r} - E_{\text{cut}} \quad \text{for} \quad r<r_c \quad \text{(and } E=0 \text{ for } r\ge r_c\text{)} \]

with \(r_c\) the cutoff and \(\varepsilon_r\) the relative permittivity of the medium. As for every pair style, the energy is shifted by its value at the cutoff, \(E_{\text{cut}}\), and the forces are not modified. The charges are the species charges. See also Short range electrostatics.

Parameter	Units	Description
`dielectric`	—	Relative dielectric constant \(\varepsilon_r\) of the medium
`shift`	—	Required, but currently unused: the energy is always shifted by the pair template
`rcut`	distance	Cutoff radius \(r_c\)

YAML syntax¶

coul_cut_compute_force:
  rcut: VALUE UNITS
  parameters: { dielectric: VALUE , shift: true }

VALUE = Physical value of the intended parameter.
UNITS = Units of the provided value that will be passed to the conversion helper for internal units conversion.

Usage examples¶

Systems with a single atomic specy

# Default variant
coul_cut_compute_force:
  parameters: { dielectric: 1.0 , shift: true }
  rcut: 12.0 ang

# Symetric variant
coul_cut_compute_force_symetric:
  parameters: { dielectric: 1.0 , shift: true }
  rcut: 12.0 ang

Systems with multiple atomic species

coul_cut_multi_force:
  rcut: 12.0 ang
  common_parameters: { dielectric: 1.0 , shift: true }
  parameters:
    - { type_a: Na , type_b: Cl , rcut: 12.0 ang , parameters: { } }
    - { type_a: Na , type_b: Na , rcut: 12.0 ang , parameters: { } }