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We present a rigorous and efficient approach to the calculation of classical lattice-dynamical quantities from simulations that do not require an explicit solution of the time evolution. We focus on the temperature-dependent vibrational spectrum. We start from the moment expansion of the relevant time-correlation function for a many-body system, and show that it can be conveniently rewritten by using a basis in which the low-order moments are diagonal. This allows us to compute the main spectral features (e.g., position and width of the phonon peaks) from thermal averages available from any statistical simulation. We successfully apply our method to a model system that presents a structural transition and strongly temperature-dependent phonons. Our theory clarifies the status of previous heuristic schemes to estimate phonon frequencies.
High quality single crystals of Bi2Se3 were grown using a modified Bridgman technique, the detailed study were carried out using Raman spectroscopy and characterized by Laue diffraction and high resolution transmission electron microscopy. Polarized
We present a vibrational dynamical mean-field theory (VDMFT) of the dynamics of atoms in solids with anharmonic interactions. Like other flavors of DMFT, VDMFT maps the dynamics of a periodic anharmonic lattice of atoms onto those of a self-consisten
We describe a coupled cluster framework for coupled systems of electrons and phonons. Neutral and charged excitations are accessed via the equation-of-motion version of the theory. Benchmarks on the Hubbard-Holstein model allow us to assess the stren
Time-dependent density-functional theory (TDDFT) is a computationally efficient first-principles approach for calculating optical spectra in insulators and semiconductors, including excitonic effects. We show how exciton wave functions can be obtaine
We present accurate optical spectra of semiconductors and insulators within a pure Kohn-Sham time-dependent density-functional approach. In particular, we show that the onset of the absorption is well reproduced when comparing to experiment. No empir