SPICA: Surface Property fItting Coarse grAined model

tSPICA Force Field

Tutorial for generating tSPICA parameters

tSPICA is an extension of SPICA designed for temperature (T ) and pressure (P ) dependence. Details of the SPICA FF can be found here. The full details of tSPICA can be found in the publication here. tSPICA scales the Lennard-Jones parameter ε_ij for the interacting pair of bead type i and j as a function of T and P with

ε_ij (T,P ) = ε_ij,SPICA + (a_1,ij )^ΔP Δε_ij,T + (a_2,ij )^ΔT Δε_ij,P

where

ε_ij,SPICA = SPICA ε_ij at 303 K and 0.1 MPa
ΔP = (P - P₀) / P₀   P₀ = 0.1 MPa
ΔT = (T - T₀) / T₀   T₀ = 303 K
Δε_ij,T = ε_1,ij ΔT + ε_2,ij (ΔT )²
Δε_ij,P = ε_3,ij ΔP + ε_4,ij (ΔP )²
ε_1,ij and ε_2,ij are the temperature dependent coefficients
ε_3,ij and ε_4,ij are the pressure dependent coefficients
a_1,ij and a_2,ij are the cross coefficients, required when T != 303 K and P != 0.1 MPa

The coefficients are fit to experimental data (typically density and surface tension). Applying this small correction improves the transferability of the original SPICA force field for non-ambient T and P conditions. All other details of the SPICA FF remain the same.