New ab initio methods
Funded by The ERC Starting Grant of Ion Errea: Discovery and Characterization of Hydrogen-Based High-Temperature Superconductors (SuperH).
Vibrational properties are crucial to describe the structural, thermodynamic, and transport properties of materials. The standard harmonic approximation assumes that ions in solids are placed at the minima of the Born-Oppenheimer potential and vibrate around these positions with phonon frequencies determined by the second-order derivatives of the potential. This picture is classical and neglects that ions are quantum objects that need to be described with a wave function. Moreover, phonon frequencies in this approach are temperature-independent and do not decay, which are intrinsic failures of this approach.
We have developed and continue developing the Stochastic Self-Consistent Harmonic Approximation (SSCHA) code that overcomes these limits. The SSCHA is a variational non-perturbative method that can calculate structural, vibrational, transport, and spectral properties of materials fully including quantum and thermal fluctuations as well as all anharmonic terms.
Since part of the work we do is focused on the prediction of the critical temperature of superconductors, we have a particular interest on the ab initio calculation of the electron-phonon interaction. We work on new methods that go beyond the standard linear approach.