Question: Who creates the computer simulation that you use for your calculations and how does the programmer know what happens at these extreme temperatures and pressures?

Lidunka Vocadlo answered on 16 Jun 2015:

@Chickenophile what a great question! Well the code I use has been developed over many many years by some clever physicists (now based in germany). The code is used for many applications, deep Earth and planetary research being only one. What I do is set up a box of atoms on the computer (usually iron for me, but it could be anything). The code uses the theory of quantum mechanics to describe the interactions between the atoms in box. As I change the dimensions of the box – make it smaller, say, the pressure goes up because I am confining the atoms to a smaller space. The code calculates the energy of the atoms in the box using quantum mechanics for each volume I choose. I then plot energy against volume, and my pressure at any volume is the gradient. Temperature is a little more tricky, but is also based on quantum mechanics to calculate the energy of my atoms in the box, which is directly related to temperature. Actually, it so happens that almost every property of my material can be worked out from the gradients of the energy. Depending on what property I calculate, I can work out different things, like how squashy a material is, or when it melts.