Electronic circular dichroism spectra using the algebraic diagrammatic construction schemes of the polarization propagator up to third order

Identification of the interchromophore interaction in the electronic absorption and circular dichroism spectra of bis-phenanthrenes

We characterize the low-lying excited electronic states of a series of bis-phenanthrenes using our newly developed diabatic scheme called the fragment particle-hole density (FPHD) method and calculate both the electronic absorption and circular dichroism (ECD) spectra using the time-dependent density functional theory (TDDFT) and the FPHD-based exciton model which couples intrachromophore local excitations (LEs) and the interchromophore charge-transfer excitations (CTEs). TDDFT treats each bis-phenanthrene as a single molecule while the mixed LE-CTE exciton model partitions the molecule into two phenanthrene-based aromatic moieties, and then applies the electronic coupling between the various quasi-diabatic states to cover the interactions. It is found that TDDFT and the mixed LE-CTE model reproduce all experimentally observed trends in the spectral profiles, and the hybridization between LE and CTE states is displayed differently in absorption and ECD spectral intensities, as it usually decreases the absorption maxima and affects the positive/negative extrema of the ECD irregularly. By comparing the results yielded by the LE-CTE model with and without the LE-CTE coupling, we identify the contribution of CTE on the main dipole-allowed transitions.

Efficient and Parallel Implementation of Real and Complex Response Functions Employing the Second-Order Algebraic-Diagrammatic Construction Scheme for the Polarization Propagator

We present the implementation of an efficient matrix-folded formalism for the evaluation of complex response functions and the calculation of transition properties at the level of the second-order algebraic-diagrammatic construction (ADC(2)) scheme. The underlying algorithms, in combination with the adopted hybrid MPI/OpenMP parallelization strategy, enabled calculations of the UV/vis spectra of a guanine oligomer series ranging up to 1032 contracted basis functions, thereby utilizing vast computational resources from up to 32,768 CPU cores. Further analysis of the convergence behavior of the involved iterative subspace algorithms revealed the superiority of a frequency-separated treatment of response equations even for a large spectral window, including 101 frequencies. We demonstrate the applicability to general quantum mechanical operators by the first reported electronic circular dichroism spectrum calculated with a complex polarization propagator approach at the ADC(2) level of theory.

Cotton-Mouton Effect Using Algebraic Diagrammatic Construction Schemes in the Intermediate State Representation Formalism

The Cotton-Mouton effect is theoretically investigated for a selected set of molecules by using a novel computational methodology based on algebraic diagrammatic construction (ADC) schemes in the intermediate state representation (ISR) formulation. Therefore, the electronic contributions to the frequency-dependent polarizabilities and, for the first time, to the magnetizabilities as well as mixed electric and magnetic hypermagnetizabilities have been computed in the ADC/ISR framework. In addition to calculation of the Cotton-Mouton constant and the birefringence, the gauge origin dependence of the computed tensors and the applied methodology are thoroughly investigated. The new ADC/ISR methodology, employing the recently presented responsefun package, is applied to a test set of Ne and small molecules (H2, HF, O2, CO2, and benzene) and compared to data from the experiment as well as other ab initio methods. The presented theoretical ab initio ADC/ISR approach is a substantial extension of the available computational methods for the investigation of complex nonlinear properties, however, with a gauge origin dependence inherent to the method that decreases with increasing perturbation order.

The Role of Spike Protein Mutations in the Infectious Power of SARS-COV-2 Variants: A Molecular Interaction Perspective

Specific S477N, N501Y, K417N, K417T, E484K mutations in the receptor binding domain (RBD) of the spike protein in the wild type SARS-COV-2 virus have resulted, among others, in the following variants: B.1.160 (20A or EU2, first reported in continental Europe), B1.1.7 (α or 20I501Y.V1, first reported in the United Kingdom), B.1.351 (β or 20H/501Y.V2, first reported in South Africa), B.1.1.28.1 (γ or P.1 or 20J/501Y.V3, first reported in Brazil), and B.1.1.28.2 (ζ, or P.2 or 20B/S484K, also first reported in Brazil). From the analysis of a set of bonding descriptors firmly rooted in the formalism of quantum mechanics, including Natural Bond Orbitals (NBO), Quantum Theory of Atoms In Molecules (QTAIM) and highly correlated energies within the Domain Based Local Pair Natural Orbital Coupled Cluster Method (DLPNO-CCSD(T)), and from a set of computed electronic spectral patterns with environmental effects, we show that the new variants improve their ability to recognize available sites to either hydrogen bond or to form salt bridges with residues in the ACE2 receptor of the host cells. This results in significantly improved initial virus⋅⋅⋅cell molecular recognition and attachment at the microscopic level, which trigger the infectious cycle.

Probing Molecular Chirality of Ground and Electronically Excited States in the UV-vis and X-ray Regimes: An EOM-CCSD Study

We present several strategies for computing electronic circular dichroism (CD) spectra across different frequency ranges at the equation-of-motion coupled-cluster singles and doubles level of theory. CD spectra of both ground and electronically excited states are discussed. For selected cases, the approach is compared with coupled-cluster linear response results as well as time-dependent density functional theory. The extension of the theory to include the effect of spin-orbit coupling is presented and illustrated by calculations of X-ray CD spectra at the L-edge.

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. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design.

Ab Initio Excited-State Electronic Circular Dichroism Spectra Exploiting the Third-Order Algebraic-Diagrammatic Construction Scheme for the Polarization Propagator

Excited-state rotatory strengths are reported for the first time at a correlated ab initio level, here with the algebraic diagrammatic construction scheme of the polarization propagator up to the third order. To demonstrate the capabilities of this computational approach, the gas phase S₁ electronic circular dichroism spectra of the bicyclic ketones (1R)-camphor, (1R)-norcamphor, and (1R)-fenchone have been calculated at the ADC(3) level of theory. Furthermore, the solution excited-state spectra of the energetically lowest conformer of R-(+)-1,1'-bi(2-naphthol) have been computed with inclusion of a polarizable continuum model at the ADC(2) level of theory.