Nuclear Energy Gradients for Internally Contracted Complete Active Space Second-Order Perturbation Theory: Multistate Extensions

Vlaisavljevich, Bess; Shiozaki, Toru

doi:10.1021/acs.jctc.6b00572

Cited by 112 publications

(191 citation statements)

References 38 publications

(111 reference statements)

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“…Finally, we applied our method to the isotropic transitionmetal HFCCs for 4 6 ] 2+ . Note that the anisotropic HFCCs are zero due to symmetry.…”

Section: Numerical Resultsmentioning

confidence: 99%

Hyperfine Coupling Constants from Internally Contracted Multireference Perturbation Theory

Shiozaki

Yanai

2016

J. Chem. Theory Comput.

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We present an accurate method for calculating hyperfine coupling constants (HFCCs) based on the complete active space second-order perturbation theory (CASPT2) with full internal contraction. The HFCCs are computed as a first-order property using the relaxed CASPT2 spin-density matrix that takes into account orbital and configurational relaxation due to dynamical electron correlation. The first-order unrelaxed spin-density matrix is calculated from one-and two-body spin-free counterparts that are readily available in the CASPT2 nuclear gradient program [M. K. MacLeod and T. Shiozaki, J. Chem. Phys. 142, 051103 (2015)], whereas the second-order part is computed directly using the newly extended automatic code generator. The relaxation contribution is then calculated from the so-called Z-vectors that are available in the CASPT2 nuclear gradient program. Numerical results are presented for the CN and AlO radicals, for which the CASPT2 values are comparable (or, even superior in some cases) to the ones computed by the coupled-cluster and density matrix renormalization group methods. The HFCCs for the hexaaqua complexes with V II , Cr III , and Mn II are also presented to demonstrate the accuracy and efficiency of our code.

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“…Finally, we applied our method to the isotropic transitionmetal HFCCs for 4 6 ] 2+ . Note that the anisotropic HFCCs are zero due to symmetry.…”

Section: Numerical Resultsmentioning

confidence: 99%

Hyperfine Coupling Constants from Internally Contracted Multireference Perturbation Theory

Shiozaki

Yanai

2016

J. Chem. Theory Comput.

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“…In the following, I and J label Slater determinants, and K, L, M, and N label reference functions. In XMS-CASPT2, the rotated reference functions are formed by diagonalizing the state-averaged Fock operator,f , within the reference space, 40,42,44 …”

Section: A Xms-caspt2 Wave Functionsmentioning

confidence: 99%

“…This MS-mixing term corresponds to the interstate coupling and can be evaluated using the methodologies described in previous work 44,47 using the PT2 Lagrangian,…”

Section: Analytical Xms-caspt2 Derivative Couplingmentioning

confidence: 99%

“…The geometries were optimized using XMS-CASPT2 with the cc-pVDZ basis set and its corresponding JKFIT basis set for density fitting unless mentioned otherwise. The so-called SS-SR contraction scheme 44 with vertical shift (0.2 E h ) was used unless otherwise specified. We searched for the MECI by the gradient projection method, 27 that uses the gradient difference and interstate coupling vectors (instead of the full derivative coupling vector).…”

Section: Numerical Examplesmentioning

confidence: 99%

“…41 Note that this extension was first proposed by Granovsky for uncontracted multireference perturbation theory. 42 Very recently, One of the authors and co-workers developed an analytical nuclear gradient program for CASPT2, 43,44 which forms the basis for the work presented herein.…”

Section: Introductionmentioning

confidence: 99%

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Analytical Derivative Coupling for Multistate CASPT2 Theory

Park

Shiozaki

2017

J. Chem. Theory Comput.

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129

167

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The probability of non-radiative transitions in photochemical dynamics is determined by the derivative couplings, the couplings between different electronic states through the nuclear degrees of freedom. Efficient and accurate evaluation of the derivative couplings is, therefore, of central importance to realize reliable computer simulations of photochemical reactions. In this work, the derivative couplings for multistate multireference second-order perturbation theory (MS-CASPT2) and its 'extended' variant (XMS-CASPT2) are studied, in which we present an algorithm for their analytical evaluation. The computational costs for evaluating the derivative couplings are essentially the same as those for calculating the nuclear energy gradients. The geometries and energies calculated with XMS-CASPT2 for small molecules at minimum energy conical intersections (MECIs) are in good agreement with those computed by multireference configuration interaction. As numerical examples, MECIs are optimized using XMS-CASPT2 for stilbene and a GFP model chromophore (the 4-para-hydroxybenzylidene-1,2-dimethyl-imidazolin-5-one anion).

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Modelling Photoionisation in Isocytosine: Potential Formation of Longer‐Lived Excited State Cations in its Keto Form

Segarra‐Martí

Bearpark

2021

ChemPhysChem

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Studying the effects of UV and VUV radiation on non-canonical DNA/RNA nucleobases allows us to compare how they release excess energy following absorption with respect to their canonical counterparts. This has attracted much research attention in recent years because of its likely influence on the origin of our genetic lexicon in prebiotic times. Here we present a CASSCF and XMS-CASPT2 theoretical study of the photoionisation of non-canonical pyrimidine nucleobase isocytosine in both its keto and enol tautomeric forms. We analyse their lowest energy cationic excited states including 2 p þ , 2 n þ O and 2 n þ N and compare these to the corresponding electronic states in cytosine. Investigating lower-energy decay pathways we find -unexpect-edly -that keto-isocytosine + presents a sizeable energy barrier potentially inhibiting decay to its cationic ground state, whereas enol-isocytosine + features a barrierless and consequently ultrafast pathway analogous to the one previously found for the canonical (keto) form of cytosine + . Dynamic electron correlation reduces the energy barrier in the keto form substantially (by ~1 eV) but it is nevertheless still present. We additionally compute the UV/Vis absorption signals of the structures encountered along these decay channels to provide spectroscopic fingerprints to assist future experiments in monitoring these intricate photo-processes.

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Nuclear Energy Gradients for Internally Contracted Complete Active Space Second-Order Perturbation Theory: Multistate Extensions

Cited by 112 publications

References 38 publications

Hyperfine Coupling Constants from Internally Contracted Multireference Perturbation Theory

Hyperfine Coupling Constants from Internally Contracted Multireference Perturbation Theory

Analytical Derivative Coupling for Multistate CASPT2 Theory

Modelling Photoionisation in Isocytosine: Potential Formation of Longer‐Lived Excited State Cations in its Keto Form

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