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

Abstract

<div> <div> <div> <p> </p><div> <div> <div> <p>Quantum Package is an open-source programming environment for quantum chemistry specially designed for wave function methods. Its main goal is the development of determinant-driven selected configuration interaction (sCI) methods and multi-reference second-order perturbation theory (PT2). The determinant-driven framework allows the programmer to include any arbitrary set of determinants in the reference space, hence providing greater method- ological freedoms. The sCI method implemented in Quantum Package is based on the CIPSI (Configuration 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 simplifies collaborative work and the development of new features. Quantum Package strives to allow easy implementation and experimentation of new methods, while making parallel computation as simple and efficient 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 efficiency. In the present manuscript, we also introduce some key new developments: i) a renormalized second-order perturbative correction for efficient 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. </p> </div> </div> </div> </div> </div> </div>

Variational Principles in Quantum Monte Carlo: The Troubled Story of Variance Minimization

“…The CIPSI calculations are performed with Quantum Package, 43 and the determinantal expansions are constructed to be eigenstates of Ŝ 2 . For the cyanine dye where ground and excited states have different symmetries, we follow two paths to construct the CIPSI expansions: (i) We perform separate expansions for the two states starting from the corresponding CASSCF(6,10) orbitals and match the variances of the CI wave functions to obtain a balanced description of the states.…”

A Density-Based Basis-Set Correction for Wave Function Theory

“…CCSD(T) energies are computed with Gaussian09 using standard threshold values, 66 while RS-DFT and exFCI calculations are performed with . 67 For the numerical quadratures, we employ the SG-2 grid. 68 Apart from the carbon dimer where we have taken the experimental equilibrium bond length (1.2425 Å), all geometries have been extracted from Ref.…”

Capturing static and dynamic correlation with ΔNO-MP2 and ΔNO-CCSD

“…Benchmark potential energy curves were obtained using a determinant-driven selected configuration interaction (sCI) method known as CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) [63][64][65] in which the energies are extrapolated to the full configuration interaction (FCI) result using multireference perturbation theory. [66][67][68] The all-electron extrapolated-FCI (exFCI) calculations were performed using Quantum Package 2.0. 68 All benchmark and ∆NO calculations were performed using the cc-pVTZ/f basis set.…”