Fermi.jl: A Modern Design for Quantum Chemistry

Abstract

Approximating molecular wave functions involves heavy numerical effort; therefore, codes for such tasks are written completely or partially in efficient languages such as C, C++, and Fortran. While these tools are dominant throughout quantum chemistry packages, the efficient development of new methods is often hindered by the complexity associated with code development. In order to ameliorate this scenario, some software packages take a dual approach where a simpler, higher-level language, such as Python, substitutes the traditional ones wherever performance is not critical. Julia is a novel, dynamically typed, programming language that aims to solve this two-language problem. It gained attention because of its modern and intuitive design, while still being highly optimized to compete with “low-level” languages. Recently, some chemistry-related projects have emerged exploring the capabilities of Julia. Herein, we introduce the quantum chemistry package Fermi.jl, which contains the first implementations of post-Hartree–Fock methods written in Julia. Its design makes use of many Julia core features, including multiple dispatch, metaprogramming, and interactive usage. Fermi.jl is a modular package, where new methods and implementations can be easily added to the existing code. Furthermore, it is designed to maximize code reusability by relying on general functions with specialized methods for particular cases. The feasibility of the project is explored through evaluating the performance of popular ab initio methods. It is our hope that this project motivates the usage of Julia within the community and brings new contributions into Fermi.jl.

Electron Correlation in the Iron(II) Porphyrin by Natural Orbital Functional Approximations

“…This work ends with some details related to the time required for the calculations. In particular, the calculations presented in this section were performed in a Julia version of the DoNOF software. , Similar codes have been reported for other electronic structure methods. As noted above, the NOF equations are solved by optimizing the NOs and ONs separately, and these steps together form an outer iteration in the optimization procedure.…”

NQCDynamics.jl: A Julia package for nonadiabatic quantum classical molecular dynamics in the condensed phase

“…Julia is not completely new to the realm of molecular simulation; of particular note are the DFTK.jl package 61 and the Fermi.jl package. 62 DFTK.jl is a plane-wave density functional theory code and Fermi.jl is a wave-functionbased quantum chemistry code. DFTK.jl has already been used to investigate new developments in the self-consistent field procedure.…”

Free and open source software for computational chemistry education

“…Access to analytical integrals greatly facilitates the implementation of post‐HF theories, and also guarantees accurate force and Hessian evaluations. Bagel 136 is a C++ program package that features, for example, analytical complete active space perturbation theory at the second order (CASPT2) nuclear energy gradients and derivative couplings, relativistic multireference wave functions based on the Dirac equation, and implementations of novel electronic structure theories. Chronus Quantum 137 is a C++ program package that focuses on the consistent treatment of time dependence and spin in the electronic wave function, as well as the inclusion of relativistic effects in said treatments. Dalton 138 is a Fortran program that specializes in molecular properties at various levels of theory, such as frequency‐dependent response properties; one‐, two‐, and three‐photon processes, etc. In addition to HF and DFT, Dalton features several post‐HF methods like multiconfigurational self‐consistent field (MCSCF) theory and coupled‐cluster theory. Ergo 139 is a C++ program for linear‐scaling HF and DFT calculations for molecules. ERKALE 77 is a C++ program implementing HF and DFT that specializes in the modeling of inelastic X‐ray spectroscopies, self‐interaction corrected DFT, as well as various orbital localization methods. e T 140 is a C++ program primarily aimed for coupled‐cluster calculations of molecular systems, which specializes in multiscale and multilevel methods, as well as modern Cholesky decomposition techniques for two‐electron integrals. Fermi.jl 141 is a Julia package for HF and post‐HF calculations. JuliaChem 142 is a Julia package for HF calculations. LSDalton 138 is a Fortran code targeted for linear‐scaling HF and DFT calculations on large molecular systems, and also includes some coupled‐cluster capabilities. MolGW 143 is a Fortran/C++ package that implements HF and DFT, but specializes in many‐body perturbation theory: the GW approximation and the Bethe–Salpeter equation. MPQC 144 is a C++ program for massively parallel quantum chemistry, which originally focused on HF and DFT but has later evolved support for post‐HF many‐body theories. NWChem 83 is a major quantum chemistry package written in Fortran and has a variety of features for both molecular and solid‐state calculations. Psi4 78 is a modular C++/Python package for HF, DFT, and various post‐HF calculations that can be used either as a traditional quantum chemistry package with simple and intuitive input files, or as Python modules for running calculations in Python. PySCF 80 is a collection of Python modules for electronic structure calculations with significant capabilities also for solid‐state simulations, including, for example, coupled‐cluster implementations for crystalline systems. PyQuante 145 is a Python package for quantum chemistry with some C extensions that emphasizes ease of understanding the code over performance. OpenMolcas 81 is a Fortran pack...…”