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Software For The Frontiers Of Quantum Chemistry: An Overview Of Developments In The Q-Chem 5 Package, Evgeny Epifanovsky, Andrew T. B. Gilbert, Xintian Feng, Joonho Lee, Yuezhi Mao, Shervin Fatehi
Software For The Frontiers Of Quantum Chemistry: An Overview Of Developments In The Q-Chem 5 Package, Evgeny Epifanovsky, Andrew T. B. Gilbert, Xintian Feng, Joonho Lee, Yuezhi Mao, Shervin Fatehi
Chemistry Faculty Publications and Presentations
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 …
Analytic Gradients For State-Averaged Multiconfiguration Pair-Density Functional Theory, Thais R. Scott, Matthew R. Hermes, Andrew M. Sand, Meagan S. Oakley, Donald G. Truhlar, Laura Gagliardi
Analytic Gradients For State-Averaged Multiconfiguration Pair-Density Functional Theory, Thais R. Scott, Matthew R. Hermes, Andrew M. Sand, Meagan S. Oakley, Donald G. Truhlar, Laura Gagliardi
Scholarship and Professional Work - LAS
Analytic gradients are important for efficient calculations of stationary points on potential energy surfaces, for interpreting spectroscopic observations, and for efficient direct dynamics simulations. For excited electronic states, as are involved in UV–Vis spectroscopy and photochemistry, analytic gradients are readily available and often affordable for calculations using a state-averaged complete active space self-consistent-field (SA-CASSCF) wave function. However, in most cases, a post-SA-CASSCF step is necessary for quantitative accuracy, and such calculations are often too expensive if carried out by perturbation theory or configuration interaction. In this work, we present the analytic gradients for multiconfiguration pair-density functional theory based on SA-CASSCF …
The Generality Of The Guga Mrci Approach In Columbus For Treating Complex Quantum Chemistry, Hans Lischka, Ron Shepard, Thomas Müller, Peter G. Szalay, Russell M. Pitzer, Adelia J. A. Aquino, Carol A. Parish, Et Al.
The Generality Of The Guga Mrci Approach In Columbus For Treating Complex Quantum Chemistry, Hans Lischka, Ron Shepard, Thomas Müller, Peter G. Szalay, Russell M. Pitzer, Adelia J. A. Aquino, Carol A. Parish, Et Al.
Chemistry Faculty Publications
The core part of the program system COLUMBUS allows highly efficient calculations using variational multireference (MR) methods in the framework of configuration interaction with single and double excitations (MR-CISD) and averaged quadratic coupled-cluster calcu- lations (MR-AQCC), based on uncontracted sets of configurations and the graphical unitary group approach (GUGA). The availability of analytic MR-CISD and MR-AQCC energy gradients and analytic nonadiabatic couplings for MR-CISD enables exciting applications including, e.g., investigations of π-conjugated biradicaloid compounds, calculations of multitudes of excited states, development of dia- batization procedures, and furnishing the electronic structure information for on-the-fly surface nonadiabatic dynamics. With fully vari- ational …
Excited States And Photochemistry Of Saturated Molecules. X. Ab Initio Calculations On The Vertical States Of Methylsilane, Mark S. Gordon
Excited States And Photochemistry Of Saturated Molecules. X. Ab Initio Calculations On The Vertical States Of Methylsilane, Mark S. Gordon
Mark S. Gordon
The vertical excitation energies are investigated for singlet and triplet states of methylsilane. To analyze the importance of Rydberg functions and of both valence and Rydbergd functions, a sequence of ten different basis sets are considered in conjuction with a single excitation configuration interaction. It is found that all of the singlet states below the first ionization potential may be characterized as Rydberg states, while there is considerable valence character in some of the low‐lying triplets. If the valence s and p functions are represented reasonably well (e.g., with a split valence basis set), the role of valence d orbitals …