The slides for all talks can be downloaded at the end of the page.
Date: 7/20, Wednesday
Speaker: Lin-Wang Wang, Materials Science Division, LBNL
Title: Large scale quantum mechanical simulations of nanosystems
Abstract: In this talk, I will present our recent works in nanostructure calculations. More specifically, I will talk about the internal electronic structure calculations of colloidal quantum dots using charge patching methods. I will also discuss the ligand surface
passivations on quantum dots and defects in quantum dots. Finally, I will present the results for the electronic structure and carrier mobility of hybrid perovskite materials.
Overall, I will show how to use electronic structure calculations to predict and
understand the properties of nanosystem.
Date: 7/22, Friday
Speaker: Chao Yang, Computational Research Division, LBNL
Title: Numerical Methods for Solving the Kohn-Sham Problem
Abstract: We will discuss numerical algorithms for solving discretized Kohn-Sham equations. We will first show that the electron density is a fixed point of a nonlinear map often known as the Kohn-Sham map, and introduce the self-consistent field (SCF) iteration, which can be viewed as a fixed point iteration for finding the solution to the Kohn-Sham problem. We will then examine the convergence properties of the SCF iteration, and discuss various strategies for improving the convergence of SCF. The complexity of the SCF iteration is dominated by the evaluation of the electron density at each iteration. The standard approach requires computing a subset of eigenvalues and eigenvectors of the Kohn-Sham Hamiltonian. We describe a number of techniques to reduce the complexity. An alternative algorithm designed to minimize the total energy of the atomistic system directly will also be presented. In this algorithm, the total energy of the system is minimized in a sequence of overlapping subspaces. The minimizer within each subspace is obtained by applying an enhanced SCF iteration to a projected nonlinear eigenvalue problem. We will show how different algorithms can be easily implemented in the KSSOLV MATLAB Toolbox.
Date: 7/25 Monday
Speaker: Bert de Jong, Computational Research Division, LBNL
Title: NWChem: Pushing the Scientific Envelope
Abstract: NWChem is providing researchers with the software resources they need for scientific discovery and technological innovation in computational molecular sciences. In this lecture we will discuss how he extensive, and often unique, suite of capabilities available in NWChem, from high-accuracy and plane wave methods to molecular dynamics, can be coupled together to tackle large and complex scientific problems while including some of the complex dynamical behavior of nature. We'll highlight some of the difficult and complex problems that are appearing on the horizon.
Date: 7/27 Wednesday
Speaker: Felipe H. da Jornada, Department of Physics, UC Berkeley
Title: Beyond DFT: predicting excited-state properties of materials using Green’s function formalisms
Abstract: Density-functional theory methods allow one to compute the ground-state energy of an interacting system exactly in terms of a functional of the ground-state electronic density. However, since DFT is a ground-state theory, the Kohn-Sham eigenvalues of the DFT cannot be directly interpreted as the quasiparticle excitation energies, even if the exact energy functional is known. In this talk, we discuss an alternative and rigorous approach to obtain excited-state properties of materials employing many-body perturbation theory techniques using Green’s function formalisms. We introduce the concept of single-particle Green’s function, which describes the propagation of an electron or a hole in the system, and which gives information on the excitation properties of systems. We discuss how these methods are connected to the commonly used GW approach to compute quasiparticle properties in materials. We also overview some computational bottlenecks associated with this method and algorithms proposed to circumvent these problems.