[gmx-developers] dH/dl variables

[Shirts, Michael (mrs5pt)]

> I try to modify GROMACS program with PLUMED extension (for metadynamic
> simulation) to handle lambda (free energy calculation parameter) as collective
> variable. I manage to apply modification to control lambda (even multiple
> lambdas from extended FEP), but i need dH/dl values for lambda driving. I
> would like to ask which variables contains such values. I have found several
> possible variables in enerdata_t struct (term,enerpart_lambda, dvdl_nonlin),
> which may contains dH/dl values, but none of them contains values which are
> exported to .xvg file.

The values that are exported to the dH/dl files are contained in the
variables:

enerd->term[F_DVDL]
enerd->term[F_DKDL]
enerd->term[F_DVDL_COUL]
enerd->term[F_DVDL_VDW]
enerd->term[F_DVDL_BONDED]
enerd->term[F_DVDL_RESTRAINT],
enerd->term[F_DVDL_TEMPERATURE] <-- not actually implemented.

which are consecutive enums (so can be looped through with
for (i = 0; i < efptNR; i++)
    something[i] = enerd->term[F_DVDL+i]

These are evaluated in the sum_dhdl function, so will be up to date anytime
after that function is called, and before the force is called again.

Note that F_DVDL contains whichever lambdas are NOT specified in the mdp.
So if there is a single lambda path, the sum of all the dhdl components will
be in F_DVDL.  

Let me know if you have any other questions.

Best,
~~~~~~~~~~~~
Michael Shirts
Assistant Professor
Department of Chemical Engineering
University of Virginia
michael.shirts at virginia.edu
(434)-243-1821