Debye-Hueckel FF
The Debye-Hueckel force field exists in two variants: with constant and relative electric permittivity of the medium. Both are described by:
\[ V = \sum \frac{q_1 q_2}{4\pi \varepsilon(r)} \frac{\exp(-r/s)}{r} \]
where the summation is over all non-local residue pairs. The variants differ in the choice of the \(\varepsilon(r)\) function.
Constant DH force field
For the constant variant, the choice of \(\varepsilon(r)\) is:
\[ \varepsilon(r) = \varepsilon_\mathrm{const} \]
Relative DH force field
For the relative variant, the choice of \(\varepsilon(r)\) is:
\[ \varepsilon(r) = A_\varepsilon r \]
Parameter file entry
# Parameters for the Debye-Hueckel (electrostatics) potential.
Debye-Hueckel:
# Whether it's enabled.
enabled: true
# Variant of the D-H potential. Options:
# - "constant", in which permittivity is constant;
# - "relative", in which permittivity is described as eps = A r, with "A" a
# permittivity factor.
variant: constant
# Screening distance for the D-H potential.
screening distance: 15.0 A
# A special cutoff distance for the electrostatics.
cutoff distance: 20.0 A
# Parameters for the constant-permittivity version.
constant variant params:
# Permittivity of the medium.
permittivity: 80.0 eps_0
# Parameters for the relative-permittivity version.
relative variant params:
# Permittivity factor, as described above.
permittivity factor: 4.0 eps_0/A