The “chain of spheres” (COS) algorithm, as part the RIJCOSX SCF procedure, approximates exchange term by performing analytic integration with respect to coordinates only one two electrons, whereas for remaining coordinates, is carried out numerically. In present work, we attempt enhance efficiency method minimizing numerical errors in COS procedure. main idea based on work Friesner and consists finding a fitting matrix, \documentclass[12pt]{minimal}\begin{document}$\mathbf...

In this work, we present a general method for predicting phosphorescence rates and spectra molecules using time-dependent density functional theory (TD-DFT) path integral approach the dynamics that relies on harmonic oscillator approximation nuclear movement. We first discuss involved in including spin-orbit coupling (SOC) among singlet triplet excited states then how to compute corrected transition dipole moments rates. investigate dependence of these some TD-DFT parameters, such as nature...

In the present work, we describe a more accurate and efficient variant of chain-of-spheres algorithm (COSX) for exchange matrix computations. Higher accuracy numerical integration is obtained with new grids that were developed using global optimization techniques. With our default grids, average absolute energy errors are much lower than 0.1 kcal/mol, which desirable to achieve “chemical accuracy.” Although size increased by roughly factor 2.5, excellent efficiency original COSX...

In this work, we present and implement the theory for calculating fluorescence rates absorption emission spectra from first principles, using path integral approach. We discuss some approximations modifications to full set of equations that improve speed numerical stability case when a large number modes are considered. New methods approximate excited state potential energy surface also discussed it is shown most purposes, these can be used instead geometry optimization obtain mentioned...

The use of back-transformed pair natural orbitals in the calculation excited state energies, ionization potentials, and electron affinities is investigated within framework equation motion coupled cluster theory its similarity transformed variant. Possible approaches to a more optimal these methods are indicated.

The chain of spheres seminumerical integration algorithm is reexamined from the point view various numerical error cancellation schemes. two sources ideas are robust fitting technique Dunlap and dealiasing concept pseudospectral methods Friesner. most efficient scheme identified found to be a generalization overlap procedure discussed earlier. It will shown that due conceptual similarity between complementary auxiliary basis functions explicitly correlated approaches methods, former can used...

The newly developed back transformed pair natural orbital based similarity equation of motion (bt-STEOM) method at the coupled cluster singles and doubles level (CCSD) is combined with an appropriate modification our earlier active space selection scheme for STEOM. resulting benchmarked valence, Rydberg, charge transfer excited states Thiel's test set other systems. bt-PNO-STEOM-CCSD gives very similar results to canonical STEOM-CCSD both singlet triplet states. It performs in a balanced...

The chain-of-spheres method (COS) for approximating two-electron integrals is applied to Hartree-Fock and density functional theory calculations of nuclear magnetic resonance chemical shielding tensors, based on gauge-including atomic orbitals. accuracy the approximation compared that resolution identity (RI) approach, using a benchmark test set 15 small molecules. Reasonable auxiliary basis sets grid sizes are selected careful investigation how each terms in self-consistent field (SCF)...

Abstract While methodological developments in the last decade made it possible to compute coupled cluster (CC) energies including excitations up a perturbative triples correction for molecules containing several hundred atoms, similar breakthrough has not yet been reported excited state computations. Accurate CC methods states are still expensive, although some promising candidates an efficient and accurate method have emerged recently. This review examines various approximation schemes with...

Boron-dipyrromethene (BODIPY) molecules form a class of fluorescent dyes known for their exceptional photoluminescence properties. Today, they are used extensively in various applications from imaging to optoelectronics. The ease altering the BODIPY core has allowed scientists synthesize dozens analogues by exploring chemical substitutions kinds or increasing length conjugated groups. However, predicting impact any change accurately is still challenge, especially as most computational...

The ability to accurately compute low-energy excited states of chlorophylls is critically important for understanding the vital roles they play in light harvesting, energy transfer, and photosynthetic charge separation. challenge quantum chemical methods arises both from intrinsic complexity electronic structure problem and, case biological models, need account protein-pigment interactions. In this work, we report calculations unprecedented accuracy Q B bands chlorophyll a. This achieved by...

In the present paper, chain of spheres exchange (COSX) approximation is applied to highest scaling terms in equation motion (EOM) coupled cluster equations with single and double excitations, particular, involving integrals four virtual labels. It found that even acceleration this term yields significant computational gains without compromising desired accuracy method. For an excitation energy calculation on a five water molecules using 585 basis functions, 9.4 times faster COSX loose grid...

In this work, we present a detailed comparison between wave-function-based and particle/hole techniques for the prediction of band gap energies semiconductors. We focus on back-transformed Pair Natural Orbital Similarity Transformed Equation Motion Coupled-Cluster (bt-PNO-STEOM-CCSD) method with Time Dependent Density Functional Theory (TD-DFT) Delta Self Consistent Field/DFT (Δ-SCF/DFT) that are employed to calculate in test set organic inorganic Throughout, have used cluster models...

This work describes a domain-based local pair natural orbital (DLPNO) implementation of the equation motion coupled cluster method for computation electron affinities (EAs) including single and double excitations. Similar to our earlier on ionization potentials (IPs), reported in this study uses ground state DLPNO framework extends it attachment problem. While full linear scaling could not be achieved as IP case, leaving Fock/Koopmans' contributions canonical basis using tighter threshold...

In this work, a domain-based local pair natural orbital (DLPNO) version of the equation motion coupled cluster theory with single and double excitations for ionization potentials (IP-EOM-CCSD) equations has been formulated implemented. The method uses ground state localized occupied virtual orbitals applies DLPNO machinery to arrive at linear scaling implementation IP-EOM-CCSD method. accuracy is controllable using truncation parameters. Using default thresholds, predicts potential (IP)...

An efficient scheme for the automatic selection of an active space similarity transformed equations motion (STEOM) coupled cluster method is proposed. It relies on state averaged configuration interaction singles (CIS) natural orbitals and makes it possible to use STEOM as a black box method. The performance new tested singlet triplet valence, charge transfer, Rydberg excited states.

The numerous existing publications on benchmarking quantum chemistry methods for excited states rarely include Charge Transfer (CT) states, although many interesting phenomena in, e.g., biochemistry and material physics involve the transfer of electrons between fragments system. Therefore, it is timely to test accuracy chemical CT as well. In this study we first propose a new benchmark set consisting dimers having low-energy states. On set, vertical excitation energy has been calculated with...

Abstract Quantum computers are special purpose machines that expected to be particularly useful in simulating strongly correlated chemical systems. The quantum computer excels at treating a moderate number of orbitals within an active space fully mechanical manner. We present phase estimation calculation on F 2 (2,2) Rigetti's Aspen‐11 QPU. While this is promising start, it also underlines the need for carefully selecting orbital spaces treated by computer. In work, scheme such automatically...

In this paper, various implementations of the analytic Hartree–Fock and hybrid density functional energy second derivatives are studied. An approximation-free four-centre implementation is presented, its accuracy rigorously analysed in terms self-consistent field (SCF), coupled-perturbed SCF (CP-SCF) convergence prescreening criteria. The CP-SCF residual norm threshold turns out to be most important these. Final choices thresholds made such that an vibrational frequencies better than 5 cm−1...

Abstract Local energy decomposition analysis provides a breakdown of the domain‐based local pair natural orbital CCSD(T) [DLPNO‐CCSD(T)] into additive contributions representing interaction between pairs user‐defined fragments. Each these fragment‐pairwise components can be further decomposed sum physically meaningful terms, such as electrostatics, dispersion, and exchange. In this study, dependence terms on basis set size, approximations used for two‐electron integrals, localization scheme...

Iron–sulfur clusters are ubiquitous electron transfer cofactors in hydrogenases. Their types and redox properties important for H 2 catalysis, but, recently, their role a protection mechanism against oxidative inactivation has also been recognized [4Fe-3S] cluster O -tolerant group 1 [NiFe] This cluster, which is uniquely coordinated by six cysteines, situated the proximity of catalytic site exhibits unusual versatility. The hydrogenase (Hase) I from Aquifex aeolicus performs two transitions...

In the present work, RIJCOSX approximation, developed earlier for accelerating SCF procedure, is applied to one of limiting factors LPNO-CCSD calculations: evaluation singles Fock term. It turns out that introduction in closed shell term causes errors below microhartree limit. If proposed procedure also combined with SCF, then a somewhat larger error occurs, but reaction energy will still remain negligible. The speedup only about 9–10 fold largest basis set applied. For case Penicillin using...

The 'chain of spheres' approximation, developed earlier for the efficient evaluation self-consistent field exchange term, is introduced here into external term higher order correlation methods. Its performance studied in specific case spin-component-scaled third-order Møller––Plesset perturbation (SCS-MP3) theory. results indicate that approximation performs excellently terms both computer time and achievable accuracy. Significant speedups over a conventional method are obtained larger...