Multi‐Configurational Reference Perturbation Theory with a CASSCF Reference Function

Lindh, Roland; Galván, Ignacio Fdez.

doi:10.1002/9781119417774.ch10

Cited by 11 publications

(18 citation statements)

References 74 publications

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“…One of the possible ways is to apply the complete active space perturbation theory (CASPT2). 13,[51][52][53][54][55] CASPT2 recovers the missing correlation of occupied and virtual orbitals and provides energies in quantitative agreement with the experiment. The higher accuracy comes at significant increase in computational cost and complex formulation of the analytic gradients.…”

Section: Qm/mm Methodologysupporting

confidence: 61%

Insight into the isomerization mechanism of retinal proteins from hybrid quantum mechanics/molecular mechanics simulations

Sen

Kar

Borin

et al. 2021

WIREs Comput Mol Sci

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The photoisomerization of retinal is a unifying primary event in the rhodopsin protein family. In vertebrate rhodopsins it is the first step in the vision process, while in the microbial rhodopsins it activates the transport of ions across the cell-membrane. This reaction is highly optimized in the protein, which is ultrafast, selective, and efficient. A great effort was directed to elucidate the mechanism due to the overall complexity of the process inside the protein. The classical one-bond-flip is too demanding in space for the confined protein cavity. Therefore, various space saving mechanisms based on the rotation of multiple double bonds have been proposed. The hybrid quantum mechanics/ molecular mechanics (QM/MM) method played an important role in the elucidation of the mechanism inside the tight protein environment. It allows to take the entire protein into account while describing the ground and excited states of retinal. The predicted mechanisms include full isomerization of two or three double bonds, a simultaneous isomerization of a single and a double bond as well as the partial rotation of bonds adjacent to the central isomerization. This review summarizes mechanistic studies in the literature and compares them.

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Section: Qm/mm Methodologysupporting

confidence: 61%

Insight into the isomerization mechanism of retinal proteins from hybrid quantum mechanics/molecular mechanics simulations

Sen

Kar

Borin

et al. 2021

WIREs Comput Mol Sci

View full text Add to dashboard Cite

show abstract

“…While this method is attractive because it is trivial to implement and does not require the calculation of the nonadiabatic coupling, one expects it to be successful only in situations where the dynamics are dominated by a single degree of freedom and/or the velocity and nonadiabatic coupling vectors are coincident. For small systems, where the total molecular system is involved in the process this technique can lead to acceptable results. − , While unprojected rescaling may succeed in vacuum, QM/MM calculations can easily involve many (thousands) degrees of freedom of which surely not all are relevant to the nonadiabatic relaxation. Simply including the kinetic energy of all the atoms (solvent + chromophore) for rescaling would functionally provide an infinite energy bath and no hops would be frustrated.…”

Section: Resultsmentioning

confidence: 99%

Nature of Hops, Coordinates, and Detailed Balance for Nonadiabatic Simulations in the Condensed Phase

Menger,

Ou,

Shao

et al. 2023

J. Phys. Chem. A

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Photoinduced processes play a crucial role in a multitude of important molecular phenomena. Accurately modeling these processes in an environment other than a vacuum requires a detailed description of the electronic states involved as well as how energy flows are coupled to the surroundings. Nonadiabatic effects must also be included in order to describe the exchange of energy between electronic and nuclear degrees of freedom correctly. In this work, we revisit the ring-opening reaction 1,3-cylohexadiene (CHD) in a solvent environment. Using our newly developed Interface for Non-Adiabatic Quantum mechanics/molecular mechanics in Solvent (INAQS) we trace the evolution of the reaction via hybrid quantum mechanics/molecular mechanics (QM/MM) surface hopping with a focus on the solvent's participation in the nonadiabatic relaxation process and the long-time approach to equilibrium. We explicitly include the MM solvent contribution to the nonadiabatic coupling vector�enabling an accurate approach to equilibrium at long times�and find that in highly multidimensional systems gradients can have little or nothing to do with the nonadiabatic couplings.

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“…However, the neglected dynamic correlation from the huge number of weakly correlated orbitals, which are outside the active space, escapes a treatment on the same level of accuracy; typically only multi-reference perturbation theory to second order represents the highest level of accuracy achievable. [31] Continuous efforts have tried to improve on this situation; examples are tailored coupled cluster, [32][33][34] combinations with short-range DFT [35][36][37][38][39][40][41] or transcorrelation [42][43][44][45][46] to treat the electron-electron cusp due to the singularity of the Coulomb interaction, to mention only a few. Already the amount of suggestions for accurate multi-configurational methods (not reflected in the list of references of this work and beyond its scope) may be taken as an indication that no universally satisfactory and generally accepted best solution has been found so far.…”

Section: Electronic Structure Modelsmentioning

confidence: 99%

Molecule‐Specific Uncertainty Quantification in Quantum Chemical Studies

Reiher

2021

Israel Journal of Chemistry

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Solving the electronic Schrödinger equation for changing nuclear coordinates provides access to the Born-Oppenheimer potential energy surface. This surface is the key starting point for almost all theoretical studies of chemical processes in electronic ground and excited states (including molecular structure prediction, reaction mechanism elucidation, molecular property calculations, quantum and molecular dynamics). Electronic structure models aim at a sufficiently accurate approximation of this surface. They have therefore become a cornerstone of theoretical and computational chemistry, molecular physics, and materials science. In this work, we elaborate on general features of approximate electronic structure models such as accuracy, efficiency, and general applicability in order to arrive at a perspective for future developments, of which a vanguard has already arrived. Our quintessential proposition is that meaningful quantum mechanical predictions for chemical phenomena require system-specific uncertainty information for each and every electronic structure calculation, if objective conclusions shall be drawn with confidence.

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Multi‐Configurational Reference Perturbation Theory with a CASSCF Reference Function

Cited by 11 publications

References 74 publications

Insight into the isomerization mechanism of retinal proteins from hybrid quantum mechanics/molecular mechanics simulations

Insight into the isomerization mechanism of retinal proteins from hybrid quantum mechanics/molecular mechanics simulations

Nature of Hops, Coordinates, and Detailed Balance for Nonadiabatic Simulations in the Condensed Phase

Molecule‐Specific Uncertainty Quantification in Quantum Chemical Studies

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