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Advances in methods and algorithms in a modern quantum chemistry program package

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TLDR
Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.
Abstract
Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.

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Multiwfn: a multifunctional wavefunction analyzer.

TL;DR: Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn, a multifunctional program for wavefunction analysis.
Journal ArticleDOI

Long-range corrected hybrid density functionals with damped atom–atom dispersion corrections

TL;DR: The re-optimization of a recently proposed long-range corrected hybrid density functional, omegaB97X-D, to include empirical atom-atom dispersion corrections yields satisfactory accuracy for thermochemistry, kinetics, and non-covalent interactions.
Journal Article

Long-Range Corrected Hybrid Density Functionals with Damped Atom-Atom Dispersion Corrections

TL;DR: Chai and Head-Gordon as discussed by the authors proposed a long-range corrected (LC) hybrid density functional with Damped Atom-Atom Dispersion corrections, which is called ωB97X-D.
References
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Journal ArticleDOI

Curvy steps for density matrix-based energy minimization: Application to large-scale self-consistent-field calculations

TL;DR: In this paper, a unitary transformation approach to avoid the diagonalization step in density functional theory calculations is developed into an algorithm that can scale linearly with molecular size, for target accuracy of 10−5 in the rms rotation gradient, the average number of matrix multiples required per self-consistent field iteration is between about 35 (STO-3G) and 50 (6-31G).
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Analytical second derivatives for excited electronic states using the single excitation configuration interaction method: theory and application to benzo[a]pyrene and chalcone

TL;DR: In this article, a semi-direct implementation of analytical second derivatives of the single excitation configuration interaction (CIS) energy is described, with a compact formulation and a semi direct implementation.
Journal ArticleDOI

Dual basis sets in calculations of electron correlation

TL;DR: In this paper, the authors evaluate correlation energies at the MP2 level of theory, using a small basis set for occupied orbitals and a larger one for the virtual space, and show that this method might be a valuable alternative for the study of systems which are currently too large for conventional methods.
Journal ArticleDOI

The imperfect pairing approximation

TL;DR: In this article, a wave function intended to model the static correlation of molecular systems is presented, which is best understood as a generalization of the perfect pairing (PP) approximation, and it is therefore termed the imperfect pairing (IP) approximation.
Journal ArticleDOI

Sparse matrix multiplications for linear scaling electronic structure calculations in an atom-centered basis set using multiatom blocks.

TL;DR: In calculations on linear alkanes, polyglycines, estane polymers, and water clusters the optimal block size is found to be between 40 and 100 basis functions, where about 55–75% of the machine peak performance was achieved on an IBM RS6000 workstation.
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