The multi-state CASPT2 method

Finley, James P.; Malmqvist, Per‐Åke; Roos, Björn O.; Serrano‐Andrés, Luis

doi:10.1016/s0009-2614(98)00252-8

Cited by 1,412 publications

(1,386 citation statements)

References 27 publications

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“…An effective Hamiltonian, constructed using second order perturbation theory, is diagonalized to obtain the final MS-CASPT2 energies. 18 Scalar relativistic effects were included using a Douglas-Kroll (DK) Hamiltonian. 19,20 The effects of spin-orbit (SO) coupling were introduced using a newly developed method based on the CASSCF State Interaction approach (CASSI), 21,22 Here, the CASSCF wave function generated for a number of electronic states are allowed to mix under the influence of a spin-orbit Hamiltonian.…”

Section: Methods and Details Of The Calculationsmentioning

confidence: 99%

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

Gagliardi¹,

Manna²,

Roos³

2003

Faraday Disc.

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An attempt has been made to study the reaction between a uranium atom and a nitrogen molecule theoretically using multiconfigurational wave functions. The C 2v part of the reaction surface has been computed for several electronic states of various spin multiplicities. The system proceeds from a neutral uranium atom in its (5f) 3 (6d)(7s) 2 , 5 L ground state to the linear molecule NUN, which has a 1 S þ g ground state and uranium in a formal U(VI) oxidation state. The effect of spin-orbit coupling has been estimated at crucial points along the reaction. These preliminary results shows that the system proceeds from a quintet state for U + N 2 , via a triplet transition state to the final closed shell molecule. An eventual energy barrier for the insertion reaction is caused by the spin-orbit coupling energy.

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Section: Methods and Details Of The Calculationsmentioning

confidence: 99%

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

Gagliardi¹,

Manna²,

Roos³

2003

Faraday Disc.

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“…49 In particular, the SS-CASPT2 method often predicts spurious CIs due to the nonorthogonality of the relevant wavefunctions. 46,49 The MS-CASPT2 method corrects this artifact by mixing these perturbed states via an effective Hamiltonian approach. In Ref.…”

Section: Computational Detailsmentioning

confidence: 99%

Photophysics of cytosine tautomers: new insights into the nonradiative decay mechanisms from MS-CASPT2 potential energy calculations and excited-state molecular dynamics simulations

Nakayama

Harabuchi

Yamazaki

et al. 2013

Phys. Chem. Chem. Phys.

111

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A comprehensive picture of the ultrafast nonradiative decay mechanisms of three cytosine tautomers (amino-keto, imino-keto, and amino-enol forms) is revealed by high-level ab initio potential energy calculations using the multistate (MS) CASPT2 method and also by on-the-fly excited-state molecular dynamics simulations employing the CASSCF method. To obtain a reliable potential energy profile along the deactivation pathways, the MS-CASPT2 method is employed even for the optimization of minimum energy structures in the excited state and conical intersection (CI) structures between the ground and excited states. In the imino (imino-keto) form, we locate a new CI structure involving the twisting of the imino group, and the decay pathway leading to this CI is found to be barrierless, suggesting a remarkably efficient deactivation of imino cytosine. In the keto (amino-keto) form, the MS-CASPT2 calculations exhibit an efficient decay path to the ethylene-like CI involving the twisting of C-C double bond in the six-membered ring, with a barrier of ~0.08 eV from the minimum of the 1 ππ* state. In the enol (amino-enol) form, three types of CIs are identified for the first time. Among them, the ethylene-like CI with a similar molecular structure to the keto form provides the most preferred deactivation pathway of enol cytosine. This pathway exhibits a higher barrier of ~0.22 eV and a higher energy of CI than those of keto cytosine. Nonadiabatic molecular dynamics simulations provide a time-dependent picture of the deactivation processes, including the excited-state lifetime of each tautomer. In particular, the decay time of the imino tautomer is predicted to be only ~100 fs. Our computational results are in remarkably good agreement with the experimental findings in recent femtosecond pump-probe photoionization spectroscopy [J. Am. Chem. Soc. 131, 16939 (2009); J. Phys. Chem. A 115, 8406 (2011)], supporting the coexistence of more than one tautomer in the photophysics of isolated cytosine and that each tautomer exhibits a different excited-state lifetime.1

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“…9,10 When multiple electronic states are nearly degenerate, special care has to be taken, because errors in the state-specific approach may arise as the CASPT2 states are generally a linear combination of the CASSCF reference states and may not be accurately approximated by a single CASSCF state. The multi-state (MS) CASPT2 approach has been derived from quasi-degenerate perturbation theory based on the Bloch wave operator formalism, which mixes different CASPT2 states by forming an effective Hamiltonian and diagonalizing it to obtain the mixing coefficients, 11,12 Recently the "extended" version of MS-CASPT2 (XMS-CASPT2) has been proposed 13,14 to rectify its failure near conical intersections and avoided crossings where its potential energy surfaces are sometimes singular. The XMS-CASPT2 method introduces a rotation of the reference CASSCF states to be used in the CASPT2 theory such that the Fock operator is diagonal within the reference space and reduces to the standard MS-CASPT2 method when this rotation is set to unit.…”

Section: Introductionmentioning

confidence: 99%

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

Vlaisavljevich

Shiozaki

2016

J. Chem. Theory Comput.

121

190

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We report the development of the theory and computer program for analytical nuclear energy gradients for (extended) multi-state complete active space perturbation theory (CASPT2) with full internal contraction. The vertical shifts are also considered in this work. This is an extension of the fully internally contracted CASPT2 nuclear gradient program, recently developed for a state-specific variant by us [MacLeod and Shiozaki, J. Chem. Phys. 142, 051103 (2015)]; in this extension, the so-called λ equation is solved to account for the variation of the multi-state CASPT2 energies with respect to the change in the amplitudes obtained in the preceding statespecific CASPT2 calculations, and the Z-vector equations are modified accordingly. The program is parallelized using the MPI3 remote memory access protocol that allows us to perform efficient one-sided communication.The optimized geometries of the ground and excited states of a copper corrole and benzophenone are presented as numerical examples. The code is publicly available under the GNU General Public License.

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The multi-state CASPT2 method

Cited by 1,412 publications

References 27 publications

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

On the reaction of a uranium atom with a nitrogen molecule: a theoretical attempt

Photophysics of cytosine tautomers: new insights into the nonradiative decay mechanisms from MS-CASPT2 potential energy calculations and excited-state molecular dynamics simulations

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

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