In this contribution to the special software-centered issue, ORCA program package is described. We start with a short historical perspective of how project began and go on discuss its current feature set. has grown into rather comprehensive general-purpose for theoretical research in all areas chemistry many neighboring disciplines such as materials sciences biochemistry. features density functional theory, range wavefunction based correlation methods, semi-empirical even force-field...

In previous publications, it was shown that an efficient local coupled cluster method with single- and double excitations can be based on the concept of pair natural orbitals (PNOs) [F. Neese, A. Hansen, D. G. Liakos, J. Chem. Phys. 131, 064103 (2009)10.1063/1.3173827]. The resulting orbital-coupled-cluster single (LPNO-CCSD) has since been proven to highly reliable efficient. For large molecules, number amplitudes determined is reduced by a factor 105–106 relative canonical CCSD calculation...

In this work, the extension of previously developed domain based local pair-natural orbital (DLPNO) singles- and doubles coupled cluster (DLPNO-CCSD) method to perturbatively include connected triple excitations is reported. The development on concept triples-natural orbitals that span joint space three pair natural (PNO) spaces electron pairs are involved in calculation a given triple-excitation contribution. truncation error very smooth can be significantly reduced through extrapolation...

Domain based local pair natural orbital coupled cluster theory with single-, double-, and perturbative triple excitations (DLPNO-CCSD(T)) is a highly efficient correlation method. It known to be accurate robust can used in black box fashion order obtain quality total energies for large molecules several hundred atoms. While previous implementations showed near linear scaling up few atoms, nonlinear steps limited the applicability of method very systems. In this work, these limitations are...

In this communication, an improved perturbative triples correction (T) algorithm for domain based local pair-natural orbital singles and doubles coupled cluster (DLPNO-CCSD) theory is reported. our previous implementation, the semi-canonical approximation was used linear scaling achieved both DLPNO-CCSD parts of calculation. work, we refer to method as DLPNO-CCSD(T0) emphasize approximation. It well-established that can predict very accurate absolute relative energies with respect parent...

The Coupled-Cluster expansion, truncated after single and double excitations (CCSD), provides accurate reliable molecular electronic wave functions energies for many systems around their equilibrium geometries. However, the high computational cost, which is well-known to scale as O(N6) with system size N, has limited its practical application small consisting of not more than approximately 20-30 atoms. To overcome these limitations, low-order scaling approximations CCSD have been intensively...

[Re(bpy)(CO)3]− is a well-established homogeneous electrocatalyst for the reduction of CO2 to CO. Recently, substitution more abundant transition metal Mn Re yielded similarly active electrocatalyst, [Mn(bpy)(CO)3]−. Compared catalyst, this catalyst operates at lower applied potential but requires presence weak acid in solution catalytic activity. In study, we employ quantum chemistry combined with continuum solvation and microkinetics examine mechanism by each catalyst. We use cyclic...

In this work, a systematic infrastructure is described that formalizes concepts implicit in previous work and greatly simplifies computer implementation of reduced-scaling electronic structure methods. The key concept sparse representation tensors using chains maps between two index sets. Sparse map can be viewed as generalization compressed row, common matrix, to tensor data. By combining few elementary operations on (inversion, chaining, intersection, etc.), complex algorithms developed,...

The local coupled cluster method DLPNO-CCSD(T) allows calculations on systems containing hundreds of atoms to be performed while typically reproducing canonical CCSD(T) energies with chemical accuracy. In this work, we present a scheme for decomposing the interaction energy between two molecules into physical meaningful contributions, providing quantification most important components interaction. method, called Local Energy Decomposition (LED), is straightforward and requires negligible...

The climbing image nudged elastic band method (CI-NEB) is used to identify reaction coordinates and find saddle points representing transition states of reactions. It can make efficient use parallel computing as the calculations discretization points, so-called images, be carried out simultaneously. In typical implementations, images are distributed evenly along path by connecting adjacent with equally stiff springs. However, for systems a high degree flexibility, this lead poor resolution...

In this work, we present a linear scaling formulation of the coupled-cluster singles and doubles with perturbative inclusion triples (CCSD(T)) explicitly correlated geminals. The implementation all post-mean-field steps utilizes SparseMaps formalism [P. Pinski et al., J. Chem. Phys. 143, 034108 (2015)]. Even for conservative truncation levels, method rapidly reaches near-linear complexity in realistic basis sets, e.g., an effective exponent 1.49 was obtained n-alkanes up to 200 carbon atoms...

[Re(bpy)(CO)3]− and [Mn(bpy)(CO)3]− are homogeneous electrocatalysts for the reduction of CO2 to CO. Their turnover frequencies depend on type Brønsted acid used, with Mn catalyst exhibiting no catalytic without added acid. In this work, we use density functional theory together continuum solvation microkinetics simulations understand these differences. The computed reproduce experimental trends. absolute numbers, differ from ones by about an order magnitude. We find that some experimentally...

We present a formulation of the explicitly correlated second-order Møller-Plesset (MP2-F12) energy in which all nontrivial post-mean-field steps are formulated with linear computational complexity system size. The two key ideas use pair-natural orbitals for compact representation wave function amplitudes and domain approximation to impose block sparsity. This development utilizes concepts sparse tensors described context based local orbital-MP2 (DLPNO-MP2) method by us recently [Pinski et...

In this work, a detailed study of spin-state splittings in three spin crossover model compounds with DLPNO-CCSD(T) is presented. The performance comparison to canonical CCSD(T) assessed detail. It was found that chemical accuracy, compared the results, are achieved when full iterative triples (T1) scheme and TightPNO settings applied relativistic effects taken into account. Having established level accuracy can be reached relative we have undertaken basis set second part study. slow...

The coupled cluster method with single-, double-, and perturbative triple excitations [CCSD(T)] is considered to be one of the most reliable quantum chemistry theories. However, steep scaling CCSD(T) has limited its application small or medium-sized systems for a long time. In our previous work, linear domain based local pair natural orbital CCSD variant (DLPNO-CCSD) been developed closed-shell open-shell. it known from extensive benchmark studies that triple-excitation contributions are...

The validity of the popular point−dipole approximation for interpretation zero-field splitting (ZFS) parameter (D-value) in EPR spectroscopy is studied. This central importance determination distances by analysis data. In this work, a detailed experimental (EPR and X-ray crystallography) theoretical study model system (2,2′,5,5′-tetra(tert-butyl)-4,4′-bis(ethoxy-carbonyl)-3,3′-bipyrrolyl-1,1′-dioxyl) was performed to understand scope limitations spectroscopy. For diradical, radical−radical...

Abstract α‐Ketoglutarate (αKG)‐dependent nonheme iron enzymes utilize a high‐spin (HS) ferrous center to couple the activation of oxygen decarboxylation cosubstrate αKG yield succinate and CO 2 , generate high‐valent ferryl species that then acts as an oxidant functionalize target CH bond. Herein detailed analysis electronic‐structure changes occur in by this enzyme was performed. The rate‐limiting step, which is identical on septet quintet surfaces, nucleophilic attack distal O atom adduct...

Since the development of chiral phosphino-oxazoline iridium catalysts, which hydrogenate unfunctionalized alkenes enantioselectively, asymmetric hydrogenation prochiral olefins has become important in production compounds. For last 10 years, details mechanism, including formal oxidation state assignment metal center and nature intermediates transition states have been debated. Various contributions given from a theoretical point view, but due to size structures, these forced rely on density...

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)...

The validity of the main approximations used in canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) DLPNO-CCSD(T), respectively) standard chemical applications is discussed. In particular, we investigate dependence results on number electrons included correlation treatment frozen-core (FC) calculations threshold governing accuracy DLPNO all-electron (AE) calculations. Initially, scalar relativistic energies for ground state atoms from Li to Rn periodic table are...

While the domain-based local pair natural orbital coupled-cluster method with singles, doubles, and perturbative triples (DLPNO-CCSD(T)) has proven instrumental for computing energies properties of large complex systems accurately, calculations on first-row transition metals a electronic structure remain challenging. In this work, we identify address two main error sources that influence DLPNO-CCSD(T) accuracy in context, namely, (i) correlation effects from 3s 3p semicore orbitals (ii)...

In this work, we tested canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) DLPNO-CCSD(T), respectively) for a set of 32 ligand exchange association/dissociation reaction enthalpies involving ionic complexes Li, Be, Na, Mg, Ca, Sr, Ba Pb(ii). Two strategies were investigated: in the former, only valence electrons included correlation treatment, giving rise to computationally very efficient FC (frozen core) approach; latter, all non-ECP AE (all electron) approach....

The linear-scaling local coupled cluster method DLPNO-CCSD(T) allows calculations on systems containing hundreds of atoms to be performed while reproducing canonical CCSD(T) energies typically with chemical accuracy (<1 kcal/mol). the is determined by two main truncation thresholds that control number electron pairs included in CCSD iterations and size pair natural orbital virtual space for each pair, respectively. While results converge smoothly toward their counterparts as are tightened,...

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...