Calendar of Events

Speaker: Yueqing Chang (UIUC) 

Abstract: 

It is challenging in first-principles calculations to elucidate the machanisms underlying phase transitions in complicated materials where multiple interactions, such as electron-electron and electron-phonon interactions, play essential roles. With the help of model Hamiltonians, one can isolate specific interaction channels and study how they compete or collaborate to generate emergent phases. In this talk, I will demonstrate a general procedure that derives accurate interacting Hamiltonians in a simple system, the hydrogen chain, using correlated many-body wave functions generated using ab-initio variational Monte Carlo. We show that the effective on-side Coulomb repulsion U and double occupancy compensate and give rise to a nearly constant effective onsite interaction contribution to the total energy as the bond length changes, which is not obvious from the ab-initio point of view. This work lays out the workflow of deriving models using the highly accurate first-principles method and I will also comment on how to establish causation of certain effective interactions during phase transition. 

Host:  Kristjan Haule