Validation of computations by high pressure measurements: Solutions to problems that experiments cannot solve

Abstract

Calculations of the properties of condensed matter systems can be crucially tested by comparison with their experimental pressure behavior. When validated by such a comparison theoretical models become reliable computer experiments and can be used to explore properties of the system which are intrinsically unobservable by experiment alone.

Three examples are given of such methods:

(i) The behavior of wurtzite indium nitride under pressure which is shown to be due to a second-order isostructural phase transition.

(ii) The instability of tetrahedrally bonded semiconductors (Ge) under pressure which turns out to be related to a second-order process.

(iii) The explanation of the lattice dynamics of a-boron at ambient conditions which can be understood only by comparison of its high pressure behavior with calculations.

Key Words:

• Calculations
• density functional theory
• phase transitions
• lattice dynamics under H.P