The CECAM electronic structure library and the modular software development paradigm

Abstract

First-principles electronic structure calculations are now accessible to a very large community of users across many disciplines, thanks to many successful software packages, some of which are described in this special issue. The traditional coding paradigm for such packages is monolithic, i.e., regardless of how modular its internal structure may be, the code is built independently from others, essentially from the compiler up, possibly with the exception of linear-algebra and message-passing libraries. This model has endured and been quite successful for decades. The successful evolution of the electronic structure methodology itself, however, has resulted in an increasing complexity and an ever longer list of features expected within all software packages, which implies a growing amount of replication between different packages, not only in the initial coding but, more importantly, every time a code needs to be re-engineered to adapt to the evolution of computer hardware architecture. The Electronic Structure Library (ESL) was initiated by CECAM (the European Centre for Atomic and Molecular Calculations) to catalyze a paradigm shift away from the monolithic model and promote modularization, with the ambition to extract common tasks from electronic structure codes and redesign them as open-source libraries available to everybody. Such libraries include “heavy-duty” ones that have the potential for a high degree of parallelization and adaptation to novel hardware within them, thereby separating the sophisticated computer science aspects of performance optimization and re-engineering from the computational science done by, e.g., physicists and chemists when implementing new ideas. We envisage that this modular paradigm will improve overall coding efficiency and enable specialists (whether they be computer scientists or computational scientists) to use their skills more effectively and will lead to a more dynamic evolution of software in the community as well as lower barriers to entry for new developers. The model comes with new challenges, though. The building and compilation of a code based on many interdependent libraries (and their versions) is a much more complex task than that of a code delivered in a single self-contained package. Here, we describe the state of the ESL, the different libraries it now contains, the short- and mid-term plans for further libraries, and the way the new challenges are faced. The ESL is a community initiative into which several pre-existing codes and their developers have contributed with their software and efforts, from which several codes are already benefiting, and which remains open to the community.

Free and Open Source Software for Computational Chemistry Education

“…104 We believe that computational chemistry will continue to transform by adopting more and more FOSS components, the Electronic Structure Library (ESL) being one of the notable pushes in this direction. 105 Welldesigned, modular FOSS components can be maintained even by a single academic group; the semi-empirical dispersion library of the Grimme group is a successful recent example. [106][107][108] We will discuss this topic further in Subsection III E.…”

“…Other types of libraries are also following suit. There is a growing ecosystem of modular electronic structure libraries as recently discussed by Oliveira et al 105 in the scope of solid state calculations. We will complement it with a brief overview of some modular open source projects that have become used within several quantum chemistry programs below.…”

Free and Open Source Software for Computational Chemistry Education

“…96 We believe that computational chemistry will continue to transform by adopting more and more FOSS components, the Electronic Structure Library (ESL) is one of the notable pushes in this direction. 97 Welldesigned, modular FOSS components can be maintained even by a single academic group; the semi-empirical dispersion library of the Grimme group is a successful recent example. [98][99][100] C. What does free and open source software offer for teaching?…”

Manifold curvature and Ehrenfest forces with a moving basis

“…[2]; for methods and programs using atomic orbitals in condensed matter see, e.g., Refs. [3][4][5][6][7][8][9]). We will restrict ourselves here to mean-field-like methods, such as Hartree-Fock or Kohn-Sham density-functional theory (DFT) [10], including their timedependent versions [11], and we will therefore use single-particle language.…”