pSPICA Force Field
pSPICA is a CG force field developed with a "polar" CG water
model. The CG modeling scheme in pSPICA is almost the same as that in the
SPICA FF. The full details of pSPICA can be found in the publication
. The pSPICA FF is developed using the polar CG water model containing
a dipole within the particle as shown below.
The polar CG water model composed of a pair of interacting sites, WO and
WH, is designed to represent three water molecules in aqueous solution.
The two sites, WO and WH, are connected by a rigid bond and carry negative
and positive partial charges, respectively. Nonbonded interaction is described
by a Lennard-Jones (LJ) interaction and the electrostatic interaction.
WH site only carries partial charge, though WO throughthe LJ interaction
using the following LJ12-5 function:
are LJ parameters. The prefactor of the LJ12-5 function is decided to have the minimum value as -εW
and to attain zero at rij
. This functional form and the LJ parameters are optimized to reproduce
the experimental density, surface tension, and dielectric permittivity
For electrostatic interactions in pSPICA, the relative dielectric constant (εr
) = 3.2 is used. Different from the SPICA FF, the charge values given in
the topology file are not scaled by the square-root of relative dielectric
) = 3.2. So the relative permittivity value should be given in the job control script explicitly.
Most of the bonded interactions and the other nonbonded interactions in
pSPICA are similar to those in the SPICA FF, though many of pair interaction
parameters were reoptimized for pSPICA water.
Thus, we have a separate parameter file for pSPICA FF.
Tutorial for pSPICA FF