How to do molecular dynamics with different isotopes of the same element?

Question

In this paper, they separated knock-on damage (originating from the collision of the beam electrons with the nucleus of the target atom) from other radiation damage mechanisms (e.g., ionization damage or chemical etching) by the comparison of ordinary (¹²C) and heavy (¹³C) graphene because any chemical effect, or ionization damage, would not distinguish between ¹²C and ¹³C. Only knock-on damage would distinguish between them. They did it experimentally.

Knock-on damage can be modeled with molecular dynamics by assigning different initial velocities to an atom hit by an electron beam.

How to do molecular dynamics with different isotopes of the same element? Is there any DFT or MD code that does it?

I searched VASP wiki, and didn't find anything about isotopes.

Answer 1

The answer is relatively simple, the neutrons do not directly contribute to anything electronically in the calculation, so the different isotopes are only different in terms of their masses / motion. To change this, simply change the default mass of the pseudopotential in VASP.