Quantum Package 2.0: An Open-Source Determinant-Driven Suite of Programs

Abstract

TOC graphical abstract antum chemistry is a discipline which relies heavily on very expensive numerical computations. e scaling of correlated wave function methods lies, in their standard implementation, between O(N 5 ) and O(e N ), where N is proportional to the system size. erefore, performing accurate calculations on chemically meaningful systems requires i) approximations that can lower the computational scaling, and ii) e cient implementations that take advantage of modern massively parallel architectures. P is an open-source programming environment for quantum chemistry specially designed for wave function methods. Its main goal is the development of determinantdriven selected con guration interaction (sCI) methods and multi-reference second-order perturbation theory (PT2). e determinant-driven framework allows the programmer to include any arbitrary set of determinants in the reference space, hence providing greater methodological freedom. e sCI method implemented in P is based on the CIPSI (Con guration Interaction using a Perturbative Selection made Iteratively) algorithm which complements the variational sCI energy with a PT2 correction. Additional external plugins have been recently added to perform calculations with multireference coupled cluster theory and range-separated density-functional theory. All the programs are developed with the IRPF90 code generator, which simpli es collaborative work and the development of new features. P strives to allow easy implementation and experimentation of new methods, while making parallel computation as simple and e cient as possible on modern supercomputer architectures. Currently, the code enables, routinely, to realize runs on roughly 2 000 CPU cores, with tens of millions of determinants in the reference space. Moreover, we have been able to push up to 12 288 cores in order to test its parallel e ciency. In the present manuscript, we also introduce some key new developments: i) a renormalized second-order perturbative correction for e cient extrapolation to the full CI limit, and ii) a stochastic version of the CIPSI selection performed simultaneously to the PT2 calculation at no extra cost.

The Quest for Highly Accurate Excitation Energies: A Computational Perspective

“…One of the strength of one of the implementation, based on the CIPSI (configuration interaction using a perturbative selection made iteratively) algorithm developed by Huron, Rancurel, and Malrieu 72 is its parallel efficiency which makes possible to run on thousands of CPU cores. 74 Thanks to these tremendous features, SCI methods deliver near FCI quality excitation energies for both singly and doubly excited states, 47,50,75,76 with an error of roughly 0.03 eV, mostly originating from the extrapolation procedure. 74 However, although the "exponential wall" is pushed back, this type of method is only applicable to molecules with a small number of heavy atoms and/or relatively compact basis sets.…”

A Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Medium Sized Molecules

“…All the SCI calculations are performed within the FC approximation using QUANTUM PACKAGE 19 where the CIPSI algorithm 3 is implemented. Details regarding this specific CIPSI implementation can be found in Refs.…”

“…The increase of computational ressources coupled to the emergence of more advanced algorithms has led to a resurgence of the selected configuration interaction (SCI) approaches [1][2][3] as an effective strategy to rapidly reach the full CI (FCI) limit at a fraction of the cost of a genuine FCI calculation thanks to a sparse exploration of the FCI space. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] This revival is especially beneficial for the calculation of transition energies between electronic states, 6,[15][16][17][18][19][20][21][22][23] as the accurate determination of these energies remains one of the great challenges faced by theoretical chemists.…”

“…24 for a recent review.) In our first work, 20 we reported TBEs for more than 100 electronic transitions of single-excitation character in organic compounds containing from one to three non-hydrogen atoms, namely C, N, O, and S. These TBEs have been obtained thanks to an efficient implementation of the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) SCI algorithm, 19 which selects the most important determinants in the FCI space using a secondorder perturbative criterion. 8 Their quality was further confirmed by equation-of-motion coupled-cluster (CC) calculations performed up to high excitation degrees.…”

Pros and Cons of the Bethe–Salpeter Formalism for Ground-State Energies

“…1. For H 2 , we take as reference the full configuration interaction (FCI) energies 104 and we also report the MP2 curve and its third-order variant (MP3), which improves upon MP2 towards FCI. RPA@HF and RPA@G 0 W 0 @HF yield almost identical results, and both significantly overestimate the FCI correlation energy, while RPAx@HF and BSE@G 0 W 0 @HF slightly over-and undershoot the FCI energy, respectively, RPAx@HF yielding the best match to FCI in the case of H 2 .…”