Quantum chemical package Jaguar: A survey of recent developments and unique features.

This paper is dedicated to the quantum chemical package Jaguar, which is commercial software developed and distributed by Schrödinger, Inc. We discuss Jaguar's scientific features that are relevant to chemical research as well as describe those aspects of the program that are pertinent to the user interface, the organization of the computer code, and its maintenance and testing. Among the scientific topics that feature prominently in this paper are the quantum chemical methods grounded in the pseudospectral approach.

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods.

Mercury Magnetic Isotope Effect: A Plausible Photochemical Mechanism.

Large mass-independent fractionation signatures in Hg have been observed in the laboratory and the environment, prompting deep questions about the chemical reasons behind these signatures. Since the relative lack of mechanistic information about Hg chemistry in the environment has precluded explanations of these isotope effects, the present study uses high-level electronic structure methods to evaluate the possible photochemical mechanisms of mass-independent isotope effects (MIEs) in HgX and CHHgX (X = Cl, Br, I, and SCH). The results show that spin-orbit coupling wipes out the potential of MIEs for Hg bound to Br or I, but that complexes involving lighter elements, HgX and CHHgX (X = Cl and SCH), have relatively small spin-orbit couplings upon photolysis.

5,10-Dimesityldiindeno[1,2-:2',1'-]phenanthrene: a stable biradicaloid derived from Chichibabin's hydrocarbon.

A diindenophenanthrene biradicaloid, formally derived from Chichibabin's hydrocarbon, is obtained in a short, scalable synthesis. The present system is electron-rich and devoid of conjugated substituents, and still exhibits very good stability under ambient conditions. The introduction of the diindeno[1,2-:2',1'-] phenanthrene ring framework results in a singlet biradicaloid system with an easily accessible triplet state (Δ = -1.

Fully Conjugated [4]Chrysaorene. Redox-Coupled Anion Binding in a Tetraradicaloid Macrocycle.

[4]Chrysaorene, a fully conjugated carbocyclic coronoid, is shown to be a low-bandgap π-conjugated system with a distinct open-shell character. The system shows good chemical stability and can be oxidized to well-defined radical cation and dication states. The cavity of [4]chrysaorene acts as an anion receptor toward halide ions with a particular selectivity toward iodides ( K = 207 ± 6 M).

Excited States of Methylene, Polyenes, and Ozone from Heat-Bath Configuration Interaction.

The electronically excited states of methylene (CH), ethylene (CH), butadiene (CH), hexatriene (CH), and ozone (O) have long proven challenging due to their complex mixtures of static and dynamic correlations. The semistochastic heat-bath configuration interaction (SHCI) algorithm, which efficiently and systematically approaches the full configuration interaction (FCI) limit, is used to provide close approximations to the FCI energies in these systems. This article presents the largest FCI-level calculation to date on hexatriene, using a polarized double-ζ basis (ANO-L-pVDZ), which gives rise to a Hilbert space containing more than 10 determinants.

Recovering dynamic correlation in spin flip configuration interaction through a difference dedicated approach.

This article introduces the restricted-active-space n-spin flip configuration interaction models, RAS(S)-SF and RAS(S,2h,2p)-SF, which provide highly correlated, yet low cost approaches for treating polyradical systems. These levels of theory add electronic degrees of freedom beyond those of previous spin flip approaches in order to achieve accurate ground and excited state energetics. The effects of additional dynamic correlation were investigated by comparing these two techniques to the prior RAS(h,p)-SF method on a variety of test systems, including multiple electronic states of methylene, tetramethyleneethane, three binuclear transition metal complexes, and a tetracene dimer.