[gmx-developers] Easy Access to MDrun Functions

[c3633]

Hi Gerrit,

I actually didn't include to much detail on the theory in the original 
e-mail, because the questions were more about the technical stuff. So 
here is a briefer description of what we're doing:

We're calculating wavepacket dynamics on a precalculated potential 
energy surface that should include all intramolecular interaction, to 
which a time-dependant Ehrenfest-Potential from the surrounding 
environment is added. Since every point on this surface corresponds to 
an arrangement of atoms in real space, the added Potential is equal to 
the solute-solvent interaction energy of that particular arrangement at 
each time-step, which can be easily calculated in gromacs at each 
time-step for each surface point.
For a time independent potential, see these publications: J. Chem. 
Theory Comput., 2015, 11 (5), pp 1987–1995 or 
http://dx.doi.org/10.1063/1.4941600.
If you want to gain a effect of the solute on the solvent, you also 
calculate the forces (in addition to the potential energies) for each 
point at each time step and propagate the molecules classically with the 
density-weighted sum of the forces while constraining the solute 
appropriately, to exclude the movement already treated with quantum 
mechanics, which i also would like to do using gromacs functions.

I hope that clarifies my original questions.
Best,
Martin.


Am 09.08.2016 12:49, schrieb Groenhof, Gerrit:
> Hi Marten,
> 
> Because it is not totally clear to me yet what you want to do, i am
> not sure if I can help.
> 
> I understand you want to do a QM simulation, using wave packet
> dynamcis? This would require more information on the (presumably
> QM/MM) potential energy surface than the on-the-fly forces?
> 
> Or is it an Ehrenfest approach, which requires you to apply the
> expectation value of the QM/MM forces on the MM atoms?
> 
> Or do you want to do Newtonian dynamics on a QM/MM potential energy
> surface, either on the-fly, or use a effective (averaged) MM
> environment
> 
> The latter would be the easiest, but I am not sure if that's what
> you're talking about.
> 
> BEst,
> 
> Gerrit
> 
> ________________________________________
> From: gromacs.org_gmx-developers-bounces at maillist.sys.kth.se
> [gromacs.org_gmx-developers-bounces at maillist.sys.kth.se] on behalf of
> c3633 [c3633 at cup.uni-muenchen.de]
> Sent: Tuesday, August 09, 2016 11:10 AM
> To: gromacs.org_gmx-developers at maillist.sys.kth.se
> Subject: [gmx-developers] Easy Access to MDrun Functions
> 
> Hi,
> 
> I am currently developing on a quantum dynamics C++-program and I would
> like to use the gromacs library to treat the environment of my system
> within a molecular dynamics framework. The current approach is to write
> an mdrun-like function that, during one time-step to first calculate
> forces on the environment-atoms and to modify them according to what
> happens in the quantum-dynamics and the to propagate the System
> according to those forces. I am fairly new to gromacs and I am just
> starting to understand the library. The functions I would need for my
> program seem to be do_force() and update_coords() from the
> legacyheaders.
> I would like to ask first, if there is a easier way to approach this,
> probably through modules like it is done for data analysis? And if not,
> how does one best generate input for those functions from a gromacs
> input file?
> 
> Thank you very much for your time,
> Martin
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