[gmx-users] acetone parameter

[Mark Abraham]

JMandumpal wrote:
>   Dear list,
> 
>           I would like to simulate aqueous acetone system using UA OPLS
> potentials. I chose the following atoms types, given below (TABLE ONE),
> for acetone, with united atom  for Methyl groups.
>                             TABLE ONE 
> ----------------------------------------------------------------------------------
> [ atoms ]
> ;  nr    type    resnr resid  atom  cgnr  charge    mass
>     1    opls_069    1  ACET    CAA    1    0.000  15.0350
>     2    opls_280    1  ACET    C_2    1    0.470  12.0110
>     3    opls_069    1  ACET    CAD    1    0.000  15.0350
>     4    opls_281    1  ACET    O_2    1  -0.470  15.9994
> -----------------------------------------------------------------------------------
> But on the other hand, when I checked the literature,  JPC
> 94, 1990, p.1683, I found out, the parameters are given in the following 
> manner, TABLE TWO :
>                                 TABLE TWO
> ************************************************************************************
> atom types  charge sigma epsilon
> CH3          0.062  3.910 0.160
> C            0.300  3.750 0.105
> O          -0.424  2.960 0.210
> **********************************************************************************
> For keeping total charge in the system  to zero, I used the opls_069 for 
> methyl group (zero charge), in my input file, compared to what has been 
> published. I would like to know whether the parameters (charge) I chose 
> is right, else which atom type I must use for methyl group.

Different models will have different charges. What is correct to use 
depends on how those models were parameterized to interact with which 
other force fields, and for what purpose they were intended. Finding 
this out and making these decisions is your job, not ours.

Mark