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DmftTriqsCthyb

This page gives some information on how to perform a DFT+DMFT calculation with the interface between ABINIT and TRIQS/CT-HYB.

Introduction

DFT+DMFT is a method made to better describe correlated systems - like \(3d\) transition metals or \(4f\) rare earths - where some electrons stay pretty localized and show strong correlation effects.

Unlike regular DFT, which is based on the electronic density, DFT+DMFT works with the Green’s function. This means it can describe one-particle excitations and gives you access to the spectral function directly.

In short, DFT+DMFT maps the complicated many-body problem of electron-electron interactions onto a simpler Anderson impurity model. In this model, the “impurity” represents the correlated orbitals on a single lattice site, while the self-consistent “bath” represents all the other electrons - either on different sites or in other orbitals. The local interactions between the impurity electrons are treated exactly, while the bath’s influence is captured through a dynamical mean field.

So, running a DFT+DMFT calculation means solving this impurity model, which is handled by an impurity solver - the most computationally demanding part of the process. ABINIT already includes its own solvers, but they use the density-density approximation, while TRIQS/CT-HYB is numerically exact.

We have built an interface between ABINIT and TRIQS/CT-HYB, so you can run fully charge self-consistent DFT+DMFT calculations on real materials. In this setup, TRIQS/CT-HYB acts as an external library that solves the impurity problem, while ABINIT handles everything else. You can activate this interface by setting dmft_solv to 6 or 7.

It is worth noting that this interface does not simply differ from ABINIT’s internal DMFT in the impurity solver - there are also important changes in the formulas, algorithms, and even some input variables used in the self-consistent loop.

Our interface was specifically designed to compute the Baym-Kadanoff functional and implements a stationary version of DFT+DMFT. It includes features like the exact double counting formula and an analytical evaluation of the high-frequency moments of the Green’s function - all of which are not available in ABINIT’s internal DMFT implementation.

compulsory:

basic:

  • dmft_solv Dynamical Mean Field Theory: choice of SOLVer

useful:

expert:

Tutorials