Exponential-6¶

Description¶

The exp6_compute_force operator calculates the normalized exponential-6 pair potential parameterized by well depth, equilibrium distance, and hardness:

\[ E(r) = \varepsilon \left[ \frac{6}{\alpha-6}\,\exp\!\big(\alpha(1 - r/r_m)\big) - \frac{\alpha}{\alpha-6}\left(\frac{r_m}{r}\right)^{6} \right] \quad \text{for} \quad r<r_c \]

with \(r_c\) the cutoff and \((\varepsilon,r_m,\alpha)\) as defined below.

Parameter	Units	Description
\(\varepsilon\)	energy	Well depth
\(r_m\)	distance	Distance at potential minimum
\(\alpha\)	—	Repulsion steepness (dimensionless)
\(r_c\)	distance	Cutoff radius

YAML syntax¶

exp6_compute_force:
  rcut: VALUE UNITS
  parameters: { epsilon: VALUE UNITS , r_m: VALUE UNITS , alpha: VALUE }

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
exp6_compute_force:
  parameters: { epsilon: 0.0100 eV , r_m: 3.80 ang , alpha: 13.0 }
  rcut: 8.0 ang

# Symetric variant
exp6_compute_force_symetric:
  parameters: { epsilon: 0.0100 eV , r_m: 3.80 ang , alpha: 13.0 }
  rcut: 8.0 ang

Systems with multiple atomic species

exp6_multi_force:
  rcut: 8.0 ang
  common_parameters: { epsilon: 0.0 , r_m: 0.0 , alpha: 0.0 }
  parameters:
    - { type_a: Ar , type_b: Ar , rcut: 8.0 ang , parameters: { epsilon: 0.0100 eV , r_m: 3.80 ang , alpha: 13.0 } }
    - { type_a: Kr , type_b: Ar , rcut: 8.0 ang , parameters: { epsilon: 0.0120 eV , r_m: 4.00 ang , alpha: 12.5 } }