Events in Physics
David O'Regan, Trinity Dublin
In contemporary first-principles atomistic simulation, the augmentation of approximate density functionals with spatially or energetically localised corrections derived from model Hamiltonians is a common approach to improving their accuracy in more strongly interacting systems. This augmentation may take place on the level of subspace-projected density-matrices, as in the widely-used density-functional theory + Hubbard U (DFT+U) method, or at the level of subspace-projected Green's functions, as in DFT + dynamical mean-field theory (DFT+DMFT). In the context of DFT+U, the Hubbard U parameter is usually interpreted either as a measure of the curvature of the total-energy with respect to subspace occupancies, deemed erroneous and due for cancellation, or as the static limit of the screened Coulomb interaction. In the context of DFT+DMFT, the latter interpretation prevails, but in both cases a generalisation to dynamical, or non-adiabatic interaction parameters U seems admissible. It remains a somewhat open question, however, how essential it is to incorporate dynamical interaction parameters, both in order to match experiment and on fundamental grounds.
Here, I will develop a viewpoint from density-functional theory, starting from the definition of the Hubbard U as an energy curvature and seeking connections with the dynamical Coulomb interaction computed using the constrained random phase approximation and sometimes used in DFT+DMFT. I will introduce a recently-developed, inexpensive and very simplistic approach to computing model dynamical Hubbard U parameters, dubbed DFT+U(ω), developed to explore these connections. This is based on a readily-available combination of static density-functional linear-response theory for the Hubbard U and methods for the dielectric function, such as time-dependent density-functional theory (TDDFT), in which case we can move beyond the random phase approximation. I will discuss different strategies for solving the resulting non-Hamiltonian models, using either a local GW approximation to the self-energy, for which I will show some preliminary results on SrVO_3, or TDDFT.
Academic Leave Diary
Physics Days
Research Group Events
.
Open Funder Deadlines
UKRI - Daphne Jackson Fellowship
.
UKRI Deadlines
Due to the implementation of a new UKRI funding system (TFS) there will be a fixed quarterly deadlines for some grants which would previously have been on open calls, this is to allow necessary system amendments and updates.
The first deadline after implementation will be 28th September 2023 and applies to those calls listed below:
EPSRC Post Doctoral Fellowship
EPSRC Working with overseas scientists