### 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} Δ

*ε*_{ij,T} + (

*a*_{2,ij} )

^{ΔT} Δ

*ε*_{ij,P}
where

*ε*_{ij,SPICA} = SPICA

*ε*_{ij} at 303 K and 0.1 MPa

Δ

*P* = (

*P - P*_{0}) /

*P*_{0} P_{0} = 0.1 MPa

Δ

*T* = (

*T - T*_{0}) /

*T*_{0} T_{0} = 303 K

Δ

*ε*_{ij,T} =

*ε*_{1,ij}* ΔT* +

*ε*_{2,ij} (Δ

*T* )

^{2}
Δ

*ε*_{ij,P} =

*ε*_{3,ij}* ΔP* +

*ε*_{4,ij} (Δ

*P* )

^{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.