HP - A code for the calculation of Hubbard parameters using density-functional perturbation theory

We introduce HP, an implementation of density-functional perturbation theory, designed to compute Hubbard parameters (on-site U and inter-site V ) in the framework of DFT+U and DFT+U+V. The code does not require the use of computationally expensive supercells of the traditional linear-response approach; instead, unit cells are used with monochromatic perturbations that significantly reduce the computational cost of determining Hubbard parameters. HP is an open-source software distributed under the terms of the GPL as a component of QUANTUM ESPRESSO. As with other components, HP is optimized to run on a variety of different platforms, from laptops to massively parallel architectures, using native mathematical libraries (LAPACK and FFTW) and a hierarchy of custom parallelization layers built on top of MPI. The effectiveness of the code is showcased by computing Hubbard parameters self-consistently for the phospho-olivine LixMn1/2Fe1/2PO4 (x = 0, 1/2, 1) and by highlighting the accuracy of predictions of the geometry and Li intercalation voltages. Program summaryProgram Title: HP CPC Library link to program files: https://doi .org /10 .17632 /xsbtkpknf7 .1 Licensing provisions: GNU General Public License v 2.0 Programming language: Fortran 95 External routines: HP is a tightly integrated component of the QUANTUM ESPRESSO distribution and requires the standard libraries linked by it: BLAS, LAPACK, FFTW, MPI.Nature of problem: Calculation of Hubbard interaction parameters for DFT+U and DFT+U+V.Solution method: Hubbard parameters are expressed in terms of the inverse response matrices to localized perturbations of the atomic occupations. The response matrices are computed using densityfunctional perturbation theory to first order (linear-response theory) in the reciprocal space, that allows to reconstruct the response to a localized perturbation (obtained from calculations in an appropriately sized supercell) as the superposition of the responses to a series of monochromatic perturbations in a primitive unit cell, thus reducing significantly the computational cost. The response matrices are computed via a self-consistent solution of the static Sternheimer equation, whose implementation does not require the calculation of any virtual states. Pseudopotentials (norm-conserving, ultrasoft, projector augmented wave) are used in conjunction with plane-wave basis sets and periodic boundary conditions. Additional comments including restrictions and unusual features: Local and semi-local exchange-correlation kernels only. Noncollinear spin-polarized formalism is not supported, only collinear spin-polarized or non-spin-polarized cases can be treated. Spin-orbit coupling cannot be used. Calculation of Hund's J is not supported. Multiple Hubbard channels per atom are not supported. The Hubbard manifold can be only constructed on atomic orbitals, both orthogonalized and non-orthogonalized, while Wannier functions (as well as other localized basis sets) are not supported. The linear-response approach we adopt here typically results in Hubbard parameters that are unphysically large for closed shell states [1]. No virtual orbitals are used, nor even calculated.The distribution file of this program can be downloaded from the QUANTUM ESPRESSO website: http:// www.quantum -espresso .org/, and the development version of this program can be downloaded via Git from the GitLab website: https://gitlab .com /QEF /q-e. Interactions with end users of the HP code happen via a mailing-list forum of QUANTUM ESPRESSO: https://www.quantum -espresso .org /forum. Documentation of the HP code is tightly coupled with the code and is done via standard code comments; different subroutines that implement different equations of the DFPT formalism contain references to the two main papers [2,3] describing in detail theory behind the implementation.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

Roberto Car, Matteo Cococcioni, Nicola Marzari, Alfredo Pasquarello, Lorenzo Paulatto, Gabriele Sclauzero

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

2009

Advanced capabilities for materials modelling with QUANTUM ESPRESSO

Oliviero Andreussi, Roberto Car, Matteo Cococcioni, Nicola Colonna, Andrea Floris, Giorgia Fugallo, Emine Küçükbenli, Nicola Marzari, Ngoc Linh Nguyen, Lorenzo Paulatto, Riccardo Sabatini, Iurii Timrov

QUANTUM ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. QUANTUM ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

Iop Publishing Ltd2017

Self-consistent continuum solvation for optical absorption of complex molecular systems in solution

Oliviero Andreussi, Nicola Marzari, Iurii Timrov

We introduce a new method to compute the optical absorption spectra of complex molecular systems in solution, based on the Liouville approach to time-dependent density-functional perturbation theory and the revised self-consistent continuum solvation model. The former allows one to obtain the absorption spectrum over a whole wide frequency range, using a recently proposed Lanczos-based technique, or selected excitation energies, using the Casida equation, without having to ever compute any unoccupied molecular orbitals. The latter is conceptually similar to the polarizable continuum model and offers the further advantages of allowing an easy computation of atomic forces via the Hellmann-Feynman theorem and a ready implementation in periodic-boundary conditions. The new method has been implemented using pseudopotentials and plane-wave basis sets, benchmarked against polarizable continuum model calculations on 4-aminophthalimide, alizarin, and cyanin and made available through the QUANTUM ESPRESSO distribution of open-source codes. (c) 2015 AIP Publishing LLC.

Amer Inst Physics2015