Version 5.0 of the ORCA quantum chemistry program suite was released in July 2021. ORCA 5.0 represents a major improvement over all previous versions of ORCA and features (1) highly improved ...performance, (2) increased numerical robustness, (3) a host of new functionality, and (4) greatly improved user friendliness. The article describes the most salient features of the program.
This article is categorized under:
Electronic Structure Theory > Ab Initio Electronic Structure Methods
Data Science > Computer Algorithms and Programming
Software > Quantum Chemistry
The article describes the features of version 5.0 of the ORCA quantum chemistry program suite
This short update provides an overview of the capabilities that have been added to the ORCA electronic structure package (version 4.0) since publication of the first article in 2012. WIREs Comput Mol ...Sci 2018, 8:e1327. doi: 10.1002/wcms.1327
This article is categorized under:
Electronic Structure Theory > Ab Initio Electronic Structure Methods
Electronic Structure Theory > Density Functional Theory
Software > Quantum Chemistry
The quantum chemistry program suite ORCA, version 4.0 is described in this article.
This article is an update of: The ORCA program system
The ORCA program system Neese, Frank
Wiley interdisciplinary reviews. Computational molecular science,
January/February 2012, Letnik:
2, Številka:
1
Journal Article
The "chain of spheres" (COS) algorithm, as part of the RIJCOSX SCF procedure, approximates the exchange term by performing analytic integration with respect to the coordinates of only one of the two ...electrons, whereas for the remaining coordinates, integration is carried out numerically. In the present work, we attempt to enhance the efficiency of the method by minimizing numerical errors in the COS procedure. The main idea is based on the work of Friesner and consists of finding a fitting matrix, Q, which leads the numerical and analytically evaluated overlap matrices to coincide. Using Q, the evaluation of exchange integrals can indeed be improved. Improved results and timings are obtained with the present default grid setup for both single point calculations and geometry optimizations. The fitting procedure results in a reduction of grid sizes necessary for achieving chemical accuracy. We demonstrate this by testing a number of grids and comparing results to the fully analytic and the earlier COS approximations. This turns out to be favourable for total and reaction energies, for which chemical accuracy can now be reached with a corresponding ~30% speedup over the original RIJCOSX procedure for single point energies. Results are slightly less favourable for the accuracy of geometry optimizations, but the procedure is still shown to yield geometries with errors well below the method inherent errors of the employed theoretical framework.
The treatment of the solvation charges using Gaussian functions in the polarizable continuum model results in a smooth potential energy surface. These charges are placed on top of the surface of the ...solute cavity. In this article, we study the effect of the solute cavity (van der Waals‐type or solvent‐excluded surface‐type) using the Gaussian charge scheme within the framework of the conductor‐like polarizable continuum model on (a) the accuracy and computational cost of the self‐consistent field (SCF) energy and its gradient and on (b) the calculation of free energies of solvation. For that purpose, we have considered a large set of systems ranging from few atoms to more than 200 atoms in different solvents. Our results at the DFT level using the B3LYP functional and the def2‐TZVP basis set show that the choice of the solute cavity does neither affect the accuracy nor the cost of calculations for small systems (< 100 atoms). For larger systems, the use of a vdW‐type cavity is recommended, as it prevents small oscillations in the gradient (present when using a SES‐type cavity), which affect the convergence of the SCF energy gradient. Regarding the free energies of solvation, we consider a solvent‐dependent probe sphere to construct the solvent‐accessible surface area required to calculate the nonelectrostatic contribution to the free energy of solvation. For this part, our results for a large set of organic molecules in different solvents agree with available experimental data with an accuracy lower than 1 kcal/mol for both polar and nonpolar solvents.
In this article, we study the effect of the solute cavity within the framework of the conductor‐like polarizable continuum model. Our solvation approach combines a treatment of the electrostatic part of the solvation energy (ΔG
solv) based on Gaussian charges, together with a nonelectrostatic contribution depending on the solvent‐accessible surface. Our results for the solvation energy of organic solutes in different solvents agree with experimental data with an accuracy lower than 1 kcal/mol.
The scope of this review is to provide a brief overview of the chemical applications carried out by local pair natural orbital coupled-electron pair and coupled-cluster methods. Benchmark tests ...reveal that these methods reproduce, with excellent accuracy, their canonical counterparts. At the same time, the speed up achieved by exploiting the locality of the electron correlation permits us to tackle chemical systems that, due to their size, would normally only be addressable with density functional theory. This review covers a broad variety of the chemical applications e.g. simulation of transition metal catalyzed reactions, estimation of weak interactions, and calculation of lattice properties in molecular crystals. This demonstrates that modern implementations of wavefunction-based correlated methods are playing an increasingly important role in applied computational chemistry.
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•Ab-initio ligand field theory –a new perspective in ligand field paradigm.•Bridging quantum chemistry and ligand-field theory.•Experimental trends in ligand field parameters are well ...reproduced.•Spin-allowed d-d transitions are reproduced with an off-set of 2000–3000cm−1.•Ab initio ligand field theory –a powerful predictive tool in molecular magnetism.•Ab initio ligand field theory –now freely available in ORCA 4.0 package.
In this work, a general, user-friendly method – ab initio ligand field theory (AILFT), is described and illustrated. AILFT allows one to unambiguously extract all ligand field parameters (the ligand field one-electron matrix VLFT, the Racah parameters B and C, and the spin-orbit coupling parameter ζ) from relatively straightforward multi-reference ab initio calculations. The method applies to mononuclear complexes in dn or fn configurations. The method is illustrated using complete active space self-consistent field (CASSCF) and N-electron valence perturbation theory (NEVPT2) calculations on a series of well documented octahedral complexes of CrIII with simple ligands such as F−, Cl−, Br−, I−, NH3 and CN−. It is shown that all well-known trends for the value of 10Dq (the spectrochemical series) are faithfully reproduced by AILFT. By comparison of B and ζ for CrIII in these complexes with the parameters calculated for the free ion Cr3+, the covalency of the Cr-ligand bond can be assessed quantitatively (the non-relativistic and relativistic nephelauxetic effects). The variation of ligand field parameters for complexes of 3d, 4d and 5d elements is studied using MCl63− (M=CrIII, MoIII, WIII) as model examples. As reflected in variations of 10Dq, B and ζ across this series, metal-ligand covalency increases from CrCl63− to MoCl63− to WCl63−. Using the angular overlap model, the one-electron parameters of the ligand field matrix are decomposed into increments for σ- and π- metal-ligand interactions. This allows for the quantification of variations in σ- and π-ligand donor properties of these ligands. Using these results, the well documented two-dimensional spectroscopic series for complexes of CrIII is quantitatively reproduced. Comparison of the results obtained using CASSCF and NEVPT2 reveals the importance of dynamic electron correlation. Finally, the limitations of the AILFT method for complexes with increasing metal-ligand covalency are analyzed and discussed.
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