Computation

KGEC: Kubo-Greenwood Electrical Conductivity

The first public version of our package to calculate Kubo-Greenwood electrical conductivity now is available. KGEC is a post-processor to QuantumEspresso. QE versions 5.1.2, 5.2.1, 5.4.0, 6.0, and 6.1 currently are supported. QE 5.2.1 compiled for use in our PROFESS@QuantumEspresso suite [see below] also is supported. KGEC provides calculation of the full complex conductivity tensor and has options for both the original KG formula (with Lorentzian) and the delta-function approximation (with both Gaussian and Lorentzian approximations for the delta function). Inter-band, intra-band, and degenerate-state contributions are calculated. The code is MPI-parallelized with respect to k-points, bands, and plane waves, and has a scheme to recover plane-wave processes for use in the bands parallelization.

The Computer Physics Communications paper that gives details of the formulae and implementation in KGEC is downloadable from our Publications page. That paper should be cited for KGEC.

We encourage you to explore KGEC. Links to the downloadable tarball and Guide for implementation and basic testing are provided in the KGEC downloads on this page. Our software is provided under GNU GPL. We welcome your comments and suggestions.

PROFESS@Quantum-Espresso

Alert (October 18, 2018): A bug was found in the way that the pressure was calculated in our modified version of PROFESS. The corrected version is in the tarball linked in the PROFESS@Quantum-Espresso downloads on this page. The bug does not affect systems with cubic symmetry but has uncertain consequences for lower symmetries.

Update (June 23, 2017): We made a minor revision so that QuantumEspresso 5.2.1 prepared for use with PROFESS@QuantumEspresso also will work with KGEC [see above]. No other changes are involved. The version 2.0.1 tarball is available in the downloads for this section.

With pleasure we announce version 2 of PROFESS@QuantumEspresso (March 2, 2016). It enables the OFDFT code PROFESS to drive ab initio MD in QuantumEspresso. The new version uses PROFESS 3.0 and QuantumEspresso 5.2.1. The package includes our temperature-dependent non-interacting and exchange-correlation single-point functionals as additions to both PROFESS and QuantumEspresso (XC functionals). The tarball also now contains a short list of known problems. If you discover any others, please let us know.

Please download and try the package. Links to the downloadable tarball and README, including implementation and basic testing information, are provided in the downloads for this section. Our software is provided under GNU GPL. For convenience, we will maintain the links to version 1 of PROFESS@QuantumEspresso for about six months, then archive that software.

Links to the PROFESS and QuantumEspresso websites are listed in the DFT Codes section on this page. To use PROFESS@QuantumEspresso, you must download those codes and comply with their respective licenses.

Details of PROFESS@QuantumEspresso are described in the article “Finite-temperature orbital-free DFT molecular dynamics: coupling PROFESS and Quantum Espresso,” Computer Physics Communications 185, 3240 (2014). The reprint is available from the Publications page. That paper should be cited for all references to PROFESS@QuantumEspresso. Other references are given in the README.

PROFESS@QuantumEspresso is installed on the University of Florida Research Computing system called HiperGator. There is a brief PROFESS@QuantumEspresso HiperGator wiki page (archived link, retrieved 2015) .

APE code modified for OFDFT

Local Download A tarball and PDF guide for our modified version of the APE code are available in the downloads for this section. APE is the “Atomic Pseudopotential Engine” originated by Oliveira and Nogueira; see Computer Physics Communications 178, 524 (2008). Modifications by K. Luo and subsequently a few more by H. Francisco make it possible to solve the orbital-free DFT version of the KS equation in the same framework as ordinary pseudopotential generation. This is subject to the usual caveat about SCF solutions of that equation; see Computer Physics Communications 183, 2519–2527 (2012), downloadable from the Publications page.

LSDA Exchange-Correlation Free Energy Subroutines

Local Download A tarball and README for our subroutines to evaluate the LSDA exchange-correlation free energy functional are available in the downloads for this section. This is the KSDT functional, which we built by fitting to path-integral Monte Carlo data. See Physical Review Letters 112, 076403 (2014) on the Publications page. Please cite that paper if you use these subroutines. They are essentially the KSDT free energy subroutines in PROFESS@Quantum-Espresso; see above. As usual, licensure is under GNU GPL.

LibXC Initialization The LibXC implementation of KSDT has an odd limitation. If initialized in the standard LibXC way, the default is zero temperature. On this page we provide initialization routines in both Fortran and C, tests, and a HOWTO file explaining usage.

Fermi-Dirac Integral Combination Analytical Fits

Certain combinations of Fermi-Dirac integrals occur so often that it is computationally effective to have analytical representations of them. Some of the older fits are not adequate to contemporary needs, especially as regards their derivatives, for which those fits usually were not designed. Here we provide Fortran 90 subroutines to evaluate several of those combinations and their derivatives with high accuracy. Links to the README and downloadable tarball are provided in the downloads for this section. Our software is provided under GNU GPL.

The fitting scheme and numerical tests are discussed in “Improved Analytical Representation of Combinations of Fermi-Dirac Integrals for Finite-temperature Density Functional Calculations,” Computer Physics Communications 192, 114–123 (2015). The reprint is available from our Publications page. That paper should be cited for all references to the F-D integral fits software.

Downloadable Pseudopotentials and PAWs

The download links on this page provide the transferable pseudopotentials and projector augmented wave data sets that we have developed for H, Li, and Al in WDM conditions. The reference papers (see Publications) are Physical Review B 86, 115101 (2012) and Physical Review E 86, 056704 (2012). Please cite them in publications that use these pseudopotentials and PAWs.

Plane-wave basis Kohn-Sham codes typically use non-local pseudopotentials. Those have different potentials for different angular-momentum KS orbitals. OFDFT has no KS orbitals, so a local pseudopotential is necessary.

Transferability refers to how well the pseudopotential, usually generated for a free atom, works in a different environment, for example a solid or molecule. In WDM, both the temperature and material density push the limits of transferability. Part of our technical work is to develop both local and non-local pseudopotentials that are temperature- and material-density transferable for the WDM regime.

DFT Codes

We have used several different DFT codes for functional development and WDM research. Our primary codes at present are PROFESS and QuantumEspresso. See PROFESS@Quantum-Espresso above. Links to those websites, as well as to other codes, are listed in the DFT Codes section on this page.

The primary requirement for using an orbital-based code at finite temperature is to have fractional occupations of eigenstates implemented with a Fermi-Dirac distribution. Many codes have this implemented, as it long has been known that use of a smearing function aids SCF convergence for metallic systems. However, such implementations may not have been tested in the WDM temperature-density domain.