Part II: Structure and Dynamics

Given the ability to calculate \(E(\mathbf{r})\), what questions can be answered? This part covers methods that interrogate the potential energy surface to determine structure and dynamics. Geometry optimisation locates minima — finding stable structures that can be compared with diffraction. Phonon calculations characterise the curvature at those minima — predicting vibrational frequencies and densities of states measurable by inelastic neutron scattering. Molecular dynamics simulates atomic motion at finite temperature, providing access to ensemble-averaged structures, diffusion coefficients, and the dynamic structure factor \(S(Q, \omega)\) measured by quasielastic neutron scattering. Each technique connects computational results directly to neutron observables.