Stumbled across an old journal a few weeks ago that suggested the equation of state for a solid could be written: V[P,T] = Vi - (C1)P + (C2)T with an internal energy: U[P,T] = (C3)T - (C2)PT C1, C2, C3 being constants of course. Does this make logical sense? It seems awfully simplified. I would assume there would be some non-linear terms in the equation of state itself (such as a T^2 or PT). Can't seem to find the paper either, but would love to look over it again if anyone is aware of what I am ranting about.