1.If the volume is fixed and without consider gravitation effect, you do not need to use Runge-Kutta method.
2. I do not understand the rest of your questions:
2) How to calculate the accuracy of volume calculation?
3) Can we find there method Monte Carlo?
4) It is there momentum?
e.g. what do you mean by "the accuracy of volume calculation"?
Why you want to find  Monte Carlo method?
momentum??? DO you maen "linear momentum"?