MARVEL Junior Seminar

Welcome to the 12th MARVEL Junior Seminar on Thursday January 18, 2018, 12:15 pm, EPFL, room MED 0 1418.

Antimo Marrazzo (EPFL, THEOS) gives a presentation on 'Prediction of a large-gap and switchable Kane-Mele quantum spin Hall insulator' and Venkat Kapil (EPFL, COSMO) on 'Accurate molecular dynamics and nuclear quantum effects at low cost using multiple time steps in real and imaginary time'. The seminar is facilitated by Quang Van Nguyen. The MARVEL Junior Seminars aim to intensify interactions between the MARVEL Junior scientists belonging to different research groups located at EPFL. The EPFL community interested in MARVEL research topics is very welcome to attend. Each seminar consists of two presentations of 25 minutes each, allowing to present on a scientific question in depth, each presentation being followed by 10 minutes for discussion.

Abstract —  Prediction of a large-gap and switchable Kane-Mele quantum spin Hall insulator - Antimo Marrazzo
Fundamental research and technological applications of topological insulators are hindered by the rarity of materials exhibiting a robust topologically non-trivial phase, especially in two dimensions. Here, by means of extensive first-principles calculations, we propose a novel quantum spin Hall insulator with a sizeable band gap of ∼0.5 eV that is a monolayer of Jacutingaite, a naturally occurring layered mineral first discovered in 2008 in Brazil and recently synthesised. This system realises the paradigmatic Kane-Mele model for quantum spin Hall insulators in a potentially exfoliable two-dimensional monolayer, with helical edge states that could be robust even beyond room temperature and that can be manipulated exploiting a unique strong interplay between spin-orbit coupling, crystal-symmetry breaking and dielectric response. 
 
Abstract —  Accurate molecular dynamics and nuclear quantum effects at low cost using multiple time steps in real and imaginary time - Venkat Kapil
Molecules and materials that contain light nuclei exhibit considerable deviations from classical behavior which are most pronounced at cryogenic temperatures, but extend up to room temperature and beyond. Properties such as dissociation of water in bulk phase or on catalytic surfaces, heat capacity, band gaps etc. are influenced by the quantum nature of nuclei. The precise description of quantum nuclear fluctuations in atomistic simulations is possible by employing path integral techniques, which involve a considerable computational overhead due to the need of simulating multiple replicas of the system. Consequently, simulations combined with advanced electronic structure methods are still prohibitive. In this talk, I will present some methodologies based on high order factorizations of the Boltzmann operator and multiple time steps in real and imaginary time, that can practically reduce the computational cost of including nuclear quantum fluctuations down to zero, while keeping interatomic interactions at high levels of electronic structure theory.