- © The Mineralogical Society Of America
Theory and computation play an increasingly important role in the field of mineral physics by allowing the scientist to probe environments, such as the deep Earth, that are challenging or impossible to access extensively by experiment. Quantum mechanical methods are often the technique of choice, usually based on Kohn-Sham density functional theory as the computationally most practical approach for solids. Although calculations at this level can already be performed on thousands of atoms (Soler et al. 2002; Cankurtaran et al. 2008), the ability to sample nuclear configuration space is often restricted. While density functional theory is typically considered the defacto standard, it is important to remember that with current functionals the results will typically be quantitatively in error with respect to experiment, with occasional qualitative errors (Bilic and Gale 2009). The strength of the method is that the errors are generally systematic and can be anticipated a priori.
Despite the ever-increasing scope of electronic structure theory for condensed phases, there are still many problems that will lie beyond their reach for the foreseeable future. Consequently, there remains a need for more approximate, but efficient, techniques to complement quantum mechanical studies. Semi-empirical Hamiltonians and tight binding represent one possibility, but if even greater speed is required then force-field methods are a valuable option. As will be discussed later, the boundaries between the aforementioned approaches are continually becoming blurred as the sophistication of force-fields increases. Beside the greater speed, force-field methods have the advantage of a clear conceptual connection between the functional form and the underlying physics. Hence much can be learnt about what physical interactions are important to describe the properties of a system.
The use of force-field methods is widespread from biological modelling to mineralogy, aided by the availability of many different programs for interatomic potential simulation. By …