Implementation of a general multireference configuration interaction procedure with analytic gradients in a semiempirical context using the graphical unitary group approach

Koslowski, Axel; Beck, Michael Edmund; Thiel, Walter

doi:10.1002/jcc.10210

Cited by 193 publications

(205 citation statements)

References 67 publications

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“…88,90 The MOs obtained from the OM2 calculation are used as input in a subsequent GUGA-MRCI calculation. 91 Conceptually, the semiempirical OM2 MO calculation already accounts for a large fraction of dynamical correlation, so that the MRCI treatment mainly needs to recover non-dynamical correlation effects. This can normally be achieved by using rather small active spaces, a small number of reference configurations, and only single and double excitations in the CI expansion (MR-CISD).…”

Section: E Om2/mrcimentioning

confidence: 99%

Assessment of approximate computational methods for conical intersections and branching plane vectors in organic molecules

Nikiforov

Gámez

Thiel

et al. 2014

The Journal of Chemical Physics

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136

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Quantum-chemical computational methods are benchmarked for their ability to describe conical intersections in a series of organic molecules and models of biological chromophores. Reference results for the geometries, relative energies, and branching planes of conical intersections are obtained using ab initio multireference configuration interaction with single and double excitations (MRCISD). They are compared with the results from more approximate methods, namely, the state-interaction state-averaged restricted ensemble-referenced Kohn-Sham method, spin-flip time-dependent density functional theory, and a semiempirical MRCISD approach using an orthogonalization-corrected model. It is demonstrated that these approximate methods reproduce the ab initio reference data very well, with root-mean-square deviations in the optimized geometries of the order of 0.1 Å or less and with reasonable agreement in the computed relative energies. A detailed analysis of the branching plane vectors shows that all currently applied methods yield similar nuclear displacements for escaping the strong non-adiabatic coupling region near the conical intersections. Our comparisons support the use of the tested quantum-chemical methods for modeling the photochemistry of large organic and biological systems. © 2014 AIP Publishing LLC. [http://dx

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Section: E Om2/mrcimentioning

confidence: 99%

Assessment of approximate computational methods for conical intersections and branching plane vectors in organic molecules

Nikiforov

Gámez

Thiel

et al. 2014

The Journal of Chemical Physics

Self Cite

136

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“…[48] This would allow the CI region to be reached along a torsional/bond-stretching (instead of pyramidalization) coordinate and make the rotation occur in a more axial fashion (see Figure 9A). In 2016, this design principle was tested by Thiel, Filatov and their co-workers, [78] who studied the S 0 and photoactive S 1 PESs of Schiff-base motor 8 in Figure 9B by means of both static calculations (at the DFT-REKS and semiempirical OM2/MRCI [79][80][81] central olefinic bond and two intermediary thermal steps, these authors found that the photoisomerization QYs of 0.4-0.6 are indeed higher than the values of 0.2-0.3 obtained for an overcrowded alkene by analogous OM2/MRCI simulations. [73] In the next subsection, we will see that there are also other Schiff-base motors whose photochemical steps NAMD simulations predict to be particularly efficient.…”

Section: And (P)-unstable-e Species Formed By Photoisomerizations Of mentioning

confidence: 99%

Quantum chemical design of rotary molecular motors

Oruganti

Wang

Durbeej

2017

Int J of Quantum Chemistry

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This tutorial review describes how recent quantum chemical calculations and non-adiabatic molecular dynamics simulations have provided valuable guidelines and insights for the design of more powerful synthetic rotary molecular motors. Following a brief overview of the various types of rotary motors synthesized to date, we present computationally identified steric and electronic approaches to significantly reduce the free-energy barriers of the critical thermal isomerization steps of chiral overcrowded alkenes, a main class of motors whose potential for many different kinds of applications is well documented. Furthermore, we describe how computational research in this field has provided new motor designs that differ from overcrowded alkenes by either (1) completing a full 3608 rotation through fewer steps, (2) exhibiting more efficient photochemical steps, or (3) requiring fewer chiral features for their function, including a design that even in the absence of a stereocenter achieves unidirectional rotary motion from two Z/E photoisomerizations alone.chirality, molecular motors, non-adiabatic molecular dynamics, photoisomerization, steric interactions | I N TR ODU C TI ONIn this tutorial review, we give an account of how quantum chemical research has contributed to advance the field of artificial molecular machines.This field [1][2][3][4][5][6][7][8][9][10][11] is devoted to the fabrication of molecular systems capable of performing the same type of machine-like functions that Nature-made protein complexes carry out in order to, among other things, propel cells, store energy in cells, equip cells with transport systems, and generate biomechanical forces. [12][13][14] Although artificial molecular machines are yet to make an impact on our everyday lives, the field is currently undergoing a rapid expansion both in terms of what man-made molecules can accomplish and the areas of expertise of the scientists drawn to the field. In many ways, this development, envisioned already in 1959 by Richard Feynman in his prophetic "There's Plenty of Room at the Bottom" lecture, [15] is testament to the groundbreaking work on the design and synthesis of molecular machines [16][17][18][19][20][21][22][23][24][25] for which Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard (Ben) L. Feringa were awarded the Nobel Prize in Chemistry 2016.While a molecular machine can be defined as "an assembly of a discrete number of molecular components designed to perform mechanical-like movements (output) as a consequence of appropriate external stimuli (input)," [2] this tutorial review focuses on the subset of such systems known as molecular motors. Loosely speaking, molecular motors are molecules that can produce net work by absorbing external energy and converting the energy into directed (non-random) mechanical motion in a controllable fashion. The ability to produce net work is the distinguishing feature of molecular motors vis-a-vis molecular switches, the latter of which sustain back-and-forth motion but not the continuous m...

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“…The structures found were then re-optimized using the semiempirical OM2 (orthogonalization model 2) method [39]. To calculate the absorption spectra, the OM2 method combined with the graphical unitary group approach (GUGA) multi-reference configuration interaction (MR-CI) [40,41] within the MNDO program [42] was used. The active space which consists of five occupied and five virtual orbitals was chosen, and all single, double, and Since the experiments were done at a temperature close to 300 K, we simulated the thermally-broadened absorption spectra.…”

Section: Computationmentioning

confidence: 99%

UV Photodissociation of Proline-containing Peptide Ions: Insights from Molecular Dynamics

Girod

Sanader

Vojković

et al. 2014

J. Am. Soc. Mass Spectrom.

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Abstract. UV photodissociation of proline-containing peptide ions leads to unusual product ions. In this paper, we report laser-induced dissociation of a series of prolinecontaining peptides at 213 nm. We observe specific fragmentation pathways corresponding to the formation of (y-2), (a + 2) and (b + 2) fragment ions. This was not observed at 266 nm or for peptides which do not contain proline residues. In order to obtain insights into the fragmentation dynamics at 213 nm, a small peptide (RPK for arginine-proline-lysine) was studied both theoretically and experimentally. Calculations of absorption spectra and non-adiabatic molecular dynamics (MD) were made. Second and third excited singlet states, S 2 and S 3 , lie close to 213 nm. Non-adiabatic MD simulation starting from S 2 and S 3 shows that these transitions are followed by C-C and C-N bond activation close to the proline residue. After this first relaxation step, consecutive rearrangements and proton transfers are required to produce unusual (y-2), (a + 2) and (b + 2) fragment ions. These fragmentation mechanisms were confirmed by H/D exchange experiments.

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Implementation of a general multireference configuration interaction procedure with analytic gradients in a semiempirical context using the graphical unitary group approach

Cited by 193 publications

References 67 publications

Assessment of approximate computational methods for conical intersections and branching plane vectors in organic molecules

Assessment of approximate computational methods for conical intersections and branching plane vectors in organic molecules

Quantum chemical design of rotary molecular motors

UV Photodissociation of Proline-containing Peptide Ions: Insights from Molecular Dynamics

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