expanded ensemble -- Adaptive Integration Method
I am attempting to include the Adaptive Integration Method (DOI: http://dx.doi.org/10.1103/PhysRevE.69.056704) to the expanded ensemble functions. I have included the files as of version 5.0.4 that I have edited. I'm at the point where my code seems to be working. I would like some feedback on the internal terms that I've chosen to use based on the calculations needed to be made. See my questions below.
Edits I have made thus far:
Names.c, Enums.h -- Added "aim" as an mdp option in the lmc move names.
State.h -- added definitions to the df_history_t structure
Expanded.c -- added AIMChooseNewLambda() method
Typedefs.c -- edited this to init the arrays I created
These are the mdp options I have created that make aim selectable, along with expanded ensemble options:
Lmc-move = aim
Nstdhdl = 1
Nstexpanded = 1
For my AIMChooseNewLambda() method I have borrowed heavily from the ChooseNewLambda() method available in expanded.c.
1 Store the current potential energy -- dfhist->store_fepot[fep_state] = enerd->term[F_EPOT]
2 Randomly choose a direction +/- lambda -- using metropolis sampler as found in ChooseNewLambda() method
3 fep_state is the current/old configuration of the system
4 lamtrial is the new configuration of the system
5 Get the energy difference between fep_state and lamtrial de = U(lamtria) - U(fep_state)
de = (double)dfhist->store_fepot[lamtrial]-(double)dfhist->store_fepot[fep_state];
6 Trapezoidal rule df = integral from lamtrial to fep_state
df = 0.5*(double)(lamtrial-fep_state)*(1.0/(double)(nlim-1.0))*(dfhist->dfavg[lamtrial]+dfhist->dfavg[fep_state]);
7 If exp(-beta*(de - df)) is greater than random(0,1), then accept and update count
8 Update fep_state
9 Calculate running average
delta = enerd->term[F_DVDL]-dfhist->dfavg[fep_state];
10 Update Free energy estimates
dfhist->dfavg[fep_state] += delta/dfhist->aim_at_lam[fep_state];
Am I using the correct term, enerd->term[F_POT], to store the potential energy of the system at fep_state?
Is there another term that has the potential energy difference between lambda states?
Am I using the correct derivative, enerd->term[F_DVDL], for the derivative of the potential energy between lambda states? -- I have already asked this question before. I'm just looking for additional confirmation.
What if someone chooses vdw-lambdas instead of fep-lambdas? Will the code need to use a different term for the derivative?
#1 Updated by Christopher Mirabzadeh almost 4 years ago
The AIM function is now working, but it's slow. It's slow because of the output of dhdl.xvg. I need a way to suppress the output of dhdl but still have access to enerd->term[F_DVDL]. The F_DVDL term needs to be calculated every step.
I have attached the new expanded.c code with the AIM function.