El coloquio del Instituto Balseiro del viernes 20/04 se titula: “Potential Energy Surfaces and Berry Phases beyond the Born-Oppenheimer Approximation: A New Perspective on the Coupled Motion of Electrons and Nuclei”. El expositor será: E.K.U. Gross. Max Planck Institute of Microstructure Physics, Halle, Germany and Hebrew University Jerusalem, Israel.
Como todos los viernes, tendrá lugar a las 14.30 hrs. en el Salón de Actos del Instituto Balseiro, en el Centro Atómico Bariloche (Av. Bustillo 9500). La entrada es gratuita y abierta a todo el público. Para ingresar, es necesario presentar el DNI en la entrada del CAB.
The Born-Oppenheimer approximation is among the most fundamental ingredients of condensed-matter theory and quantum chemistry. This approximation not only makes calculations feasible, it also provides us with an intuitive picture of chemical reactions. Yet it is an approximation, and some of the most fascinating phenomena, such as the process of vision, photovoltaic dynamics, as well as phonon-driven superconductivity occur in the regime where the Born-Oppenheimer approximation breaks down. To tackle such situations we deduce an exact factorization of the full electron-nuclear wavefunction into a purely nuclear part and a many-electron wavefunction which parametrically depends on the nuclear configuration and which has the meaning of a conditional probability amplitude. The equations of motion for these wavefunctions lead to a unique definition of exact potential energy surfaces as well as exact geometric phases. We discuss a case where the exact molecular Berry phase vanishes although there is a non-trivial Berry phase for the same system in Born-Oppenheimer approximation, implying that in this particular case the Born-Oppenheimer Berry phase is an artifact. In the time-domain, the full nuclear dynamics, including all non-adiabatic effects, is described by the motion of a nuclear wavepacket on a single, but time-dependent potential energy surface. Starting from this framework, we deduce a novel mixed-quantum-classical algorithm which neither requires surface hopping nor decoherence corrections. The power of the method will be demonstrated with a simulation of the laser-induced ring opening of the oxirane molecule.
Dr. Hardy Gross received his MA (1976) and his PhD (1980) at the Goethe University in Frankfurt, Germany. After a postdoctoral stay and a Heisenberg Professorship at the University of California, Santa Barbara, where he worked with Walter Kohn, he returned to Germany in 1990 to become a Fiebiger Professor at the University of Würzburg. In 2001 he moved to Berlin to become Chair of Theoretical Physics at the Free University Berlin, and since 2009 he is the Director of the Theory Department at the Max Planck Institute of Microstructure Physics in Halle (Saale), Germany. He was Managing Director of this Institute from 2013-2016. Since 2017 he is also Professor of Chemistry at the Hebrew University Jerusalem. In 2003-2004 he was a foreign fellow at Trinity College, Cambridge, UK, and 2013-2016 he was Visiting Research Professor at the University of Hong Kong. He served as president of the Council of CECAM (Centre Europeen de Calcul Atomique et Moleculaire) from 2004 to 2008. Among his main recognitions are the 2004 Schlumberger Award at Cambridge University, the 2015 Tsung Ming Tu Prize (the highest distinction given by the Government of Taiwan to foreign scholars), the 2016 Bernie Alder CECAM prize (the most prestigious European distinction, awarded every 3 years, in the field of Computer Simulations) and he received an ERC Advanced Grant in 2018. He published 270 scientific articles and co-authored two textbooks. His primary field of research is electronic structure theory. He laid the foundation of time-dependent density functional theory with a theorem, now known as Runge-Gross theorem, developed a parameter-free ab-initio theory of phonon-driven superconductivity, and his most recent research focus has been the description of non-adiabatic dynamics in molecules and solids.