The splitting method of BAOAB integrator

[yongyouhe]

Hi,

I noticed that the GHMCIntegrator uses the "O{VRV}O" splitting method, while the LangevinIntegrator uses the "VRORV" splitting method. I am confusing the difference between "O{VRV}O" and "VRORV." Would it be possible for the GHMCIntegrator to produce the same results if it adopted the "{VRORV}" splitting method instead?

If I want to combine the generalized hybrid Monte Carlo with MTSLangevin, which splitting method would be better?

Additionally, I noticed that in the OpenMM MSTLangevinIntegrator code, the v is not computed in the first "R" step (detailed code shown below). Why is this the case?
code link

    if len(groups) == 1:
        self.addComputePerDof("x", "x+(dt/"+str(2*substeps)+")*v")

        self.addComputePerDof("v", "a*v + b*sqrt(kT/m)*gaussian")
        self.addComputePerDof("x", "x+(dt/"+str(2*substeps)+")*v")
        self.addComputePerDof("x1", "x")
        self.addConstrainPositions();
        self.addComputePerDof("v", "v+(x-x1)/(dt/"+str(substeps)+")");

Looking forward to your reply!
Best regards.

[yongyouhe]

For example, if I want to combine the generalized hybrid Monte Carlo with MTSLangevin for force group [(0,2), (1,1)], should the splitting method be "O{V1 V0 R V0 V0 R V0 V1}O"?

Appreciate it if someone could address my question.