[gmx-users] inconsistent energies

[Mark Abraham]

On 8/01/2011 12:10 AM, Vlad Isaev wrote:
> Hi,
>
> I want to calculate the energy of a peptide. No minimization, or md, 
> just the energy at 0 K. I use this input:
>
> integrator               = steep
> nsteps                   = 0
> nstenergy                = 1
> nstlist                  = 0
> ns_type                  = simple
> pbc                      = no
> rlist                    = 0
> rcoulomb                 = 0
> rvdw                     = 0
>
>
> I get:
>
> Potential Energy  = -1.1744482e+02
>
> Changing steep to cg changes the potential energy even though nsteps=0:
>
> Potential Energy  = -1.2410449e+02
>
> The corresponding energy from AMBER10 is : -1.20172848e+02 (conversion 
> factor 4.184).
>
> Any ideas why these are so different?

That's pretty weird. Please double check that you were really using the 
same input coordinates to grompp (and that mdrun wasn't picking up a 
checkpoint file).

Mark