Recent progress with large-scale ab initio calculations: the CONQUEST code

TL;DR

The paper discusses recent advancements in the extsc{Conquest} code, enabling efficient large-scale density functional theory calculations with linear scaling, capable of handling systems over 10,000 atoms across various levels of precision.

Contribution

It introduces practical extsc{Conquest} code developments that achieve linear scaling DFT calculations on parallel computers for large systems.

Findings

Demonstrated extsc{Conquest} handling over 10,000 atoms.

Showcased multi-level precision calculations from tight-binding to full ab initio.

Presented techniques for consistent ionic force calculations at all levels.

Abstract

While the success of density functional theory (DFT) has led to its use in a wide variety of fields such as physics, chemistry, materials science and biochemistry, it has long been recognised that conventional methods are very inefficient for large complex systems, because the memory requirements scale as $N^2$ and the cpu requirements as $N^3$ (where $N$ is the number of atoms). The principles necessary to develop methods with linear scaling of the cpu and memory requirements with system size ($\mathcal{O}(N)$ methods) have been established for more than ten years, but only recently have practical codes showing this scaling for DFT started to appear. We report recent progress in the development of the \textsc{Conquest} code, which performs $\mathcal{O}(N)$ DFT calculations on parallel computers, and has a demonstrated ability to handle systems of over 10,000 atoms. The code can be run at different levels of precision, ranging from empirical tight-binding, through \textit{ab initio} tight-binding, to full \textit{ab initio}, and techniques for calculating ionic forces in a consistent way at all levels of precision will be presented. Illustrations are given of practical \textsc{Conquest} calculations in the strained Ge/Si(001) system.