Confusion Regarding Volume Transfer for GEMC II

[ruyeli]

Hello,

Following up on my previous issue (#528 ), I have another question regarding the calculation for volume transfer in Volumetransfer.h.

In the VolumeTransfer::GetCoeff() function, I notice the following code:

  if (GEMC_KIND == mv::GEMC_NVT) {
    for (uint b = 0; b < 2; ++b) {
      if(isOrth)
        coeff *= pow(newDim.volume[bPick[b]] / boxDimRef.volume[bPick[b]],
                     (double)molLookRef.NumInBox(bPick[b]));
      else
        coeff *= pow(newDimNonOrth.volume[bPick[b]] / boxDimRef.volume[bPick[b]],
                     (double)molLookRef.NumInBox(bPick[b]));
    }

In the code above, the power term uses molLookRef.NumInBox(bPick[b]) directly. However, in the theoretical formulation of the acceptance ratio in textbooks like Understanding Molecular Simulation, the power term includes an additional +1. This discrepancy leads me to wonder if there might be a slight deviation from the intended formula.

For reference, please see the attached figure illustrating the acceptance ratio from the textbook:

If the code is correct as it is, I’d appreciate any clarification on the equations or algorithms it follows. Understanding this aspect of the implementation would greatly help deepen my comprehension and be beneficial to my work.

Thank you for your time and for providing this valuable tool!