Ab initio lattice dynamics: Methods, results, and applications

Abstract

The density-functional perturbation theory (DFPT) introduced by Baroni and co-workers, allows for the ab initio (parameter-free) calculation of lattice-dynamical properties. The method is sketched and set into relation to other approaches. Biased by personal view, we present current applications of the DFPT to the calculation of the harmonic lattice dynamics, i.e., phonon dispersion curves and eigenvectors for various systems ranging from insulators to metals. Since the phonon frequencies and eigenvectors are in extremely good agreement with the available experimental data the calculations have a very reliable predictive power for a number of crystals which have not yet been experimentally investigated. Within and beyond the harmonic approximation several thermal quantities can be calculated such as heat capacity, Debye-Waller factors, cumulants (for EXAFS experiments), and others, often with a precision exceeding the experimental one. Last but not least, the combination of the results of the DFPT with frozen-phonon techniques allows a straightforward calculation of nonlinear coefficients of the lattice potential such as anharmonic coupling coefficients, nonlinear dipole-moment coefficients, and Raman coupling constants. Within this context, numerical results are presented for Gruneisen constants, thermal expansion coefficients, various pressure and temperature effects, and Raman and infrared two-phonon spectra.