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:
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2) How to calculate the accuracy of volume calculation?
3) Can we find there method Monte Carlo?
4) It is there momentum?
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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"?