Re: Alchemy Shift Coefficient at Low Density Regime (TI)

From: Brian Radak (
Date: Thu Feb 05 2015 - 13:44:14 CST

Hi Javad,

The shift parameter is actually a squared distance, so the default
"distance" is ~0.22 nm.

There have been very few systematic studies of softcore potential
parameters, so I think you would be hard pressed for someone to strongly
recommend a value beyond the default. In the gas phase though, I would
suspect that a softcore potential is not necessary (that is just a naive
opinion though).


On 02/04/2015 02:58 AM, JAVAD NOROOZI wrote:
> Hi all,
> The recommended value for the soft core parameter (Alchemy Shift
> Coeff) is 0.5nm . Does this is recommended for liquid (solution) phase
> simulations?
> I am interested in solvation free energy in gas-like density regimes,
> where interatomic distances are much larger than liquid phase and
> shifting vdw distance might prevent proper sampling of the phase space.
> I am trying to get solvation free enrgy of aromatics in super-critcal
> CO2, at lower densities result deviate from experiment (around 0.6
> Kcal/mol), could this be atributed to soft core parameter or weak
> performance of the force field in gas-like densities(because most
> force field are parametrize to performe in liquid phase).
> Javad
> ________________________________________________
> /Chemical and Petroleum Engineering Department,/
> /Sharif University of Technology , Tehran, IRAN/

Brian Radak
Postdoctoral Scholar
Gordon Center for Integrative Science, W323A
Department of Biochemistry & Molecular Biology
University of Chicago
929 E. 57th St.
Chicago, IL 60637-1454
Tel: 773/834-2812

This archive was generated by hypermail 2.1.6 : Thu Dec 31 2015 - 23:21:38 CST