A computational approach to the direct configuration interaction method is described. The formulated using calculus of generators unitary group. simple structure generator matrices within harmonic excitation level scheme exploited give a that competitive with traditional approaches. new for basis set truncation in case partial devised employing orbital populations. It also shown block leads definition order parameter perturbation methods which both effective and convenient.

In this paper we use ab initio multiconfigurational second-order perturbation theory to establish the intrinsic photoisomerization path model of retinal chromophores. This is accomplished by computing ground state (S(0)) and first two singlet excited-state (S(1), S(2)) energies along rigorously determined coordinate rhodopsin chromophore 4-cis-gamma-methylnona-2,4,6,8-tetraeniminium cation bacteriorhodopsin all-trans-hepta-2,4, 6-trieniminium in isolated conditions. The computed S(2) S(1)...

Singlet fluorescence lifetimes of adenosine, cytidine, guanosine, and thymidine, determined by femtosecond pump−probe spectroscopy (Pecourt, J.-M. L.; Peon, J.; Kohler, B. J. Am. Chem. Soc. 2000, 122, 9348. Pecourt, 2001, 123, 10370), show that the excited states produced 263 nm light in these nucleosides decay subpicosecond range (290−720 fs). Ultrafast radiationless to ground state greatly reduces probability photochemical damage. In this work we present a theoretical study isolated...

Atomistic QM/MM simulations have been carried out on the complete photocycle of Photoactive Yellow Protein, a bacterial photoreceptor, in which blue light triggers isomerization covalently bound chromophore. The "chemical role" protein cavity control photoisomerization step has elucidated. Isomerization is facilitated due to preferential electrostatic stabilization chromophore's excited state by guanidium group Arg52, located just above negatively charged chromophore ring. In vacuo does not...

The minimum energy path for photoisomerization of the minimal retinal protonated Shiff base model tZt-penta-3,5-dieniminium cation (cis-C5H6NH2+) is computed using MC−SCF and multireference Møller−Plesset methods. results show that, upon excitation to spectroscopic state, this molecule undergoes a barrierless relaxation toward configuration where excited ground states are conically intersecting. intersection point has ∼80° twisted central double bond which provides route fully efficient...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAn MC-SCF study of the S1 and S2 photochemical reactions benzeneIan J. Palmer, Ioannis N. Ragazos, Fernando Bernardi, Massimo Olivucci, Michael A. RobbCite this: Am. Chem. Soc. 1993, 115, 2, 673–682Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://pubs.acs.org/doi/10.1021/ja00055a042https://doi.org/10.1021/ja00055a042research-articleACS PublicationsRequest reuse...

In a recent paper (G. Worth, P. Hunt and M. Robb, J. Phys. Chem. A, 2003, 107, 621), we used surface hopping direct dynamics calculations to study the molecular of butatriene radical cation in X/A manifold, which is coupled by conical intersection. Here, present first using novel algorithm, again this ideal test system. The based on powerful multi-configuration time-dependent Hartree (MCTDH) wavepacket propagation method, uses variational basis frozen Gaussian functions that optimally...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA conical intersection mechanism for the photochemistry of butadiene. A MC-SCF studyMassimo Olivucci, Ioannis N. Ragazos, Fernando Bernardi, and Michael A. RobbCite this: J. Am. Chem. Soc. 1993, 115, 9, 3710–3721Publication Date (Print):May 1, 1993Publication History Published online1 May 2002Published inissue 1 1993https://doi.org/10.1021/ja00062a042RIGHTS & PERMISSIONSArticle Views1065Altmetric-Citations176LEARN ABOUT THESE METRICSArticle Views...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTAb Initio Photoisomerization Dynamics of a Simple Retinal Chromophore ModelThom Vreven, Fernando Bernardi, Marco Garavelli, Massimo Olivucci, Michael A. Robb, and H. Bernhard SchlegelView Author Information Department Chemistry, King's College London WC2R 2LS, United Kingdom Dipartimento di Chimica "G.Ciamician" dell' Università Bologna Via Selmi 2, 40126 Bologna, Italy Wayne State University, Detroit, Michigan 48202 Cite this: J. Am. Chem....

We address the possibility of populating lowest triplet state cytosine by an "intrinsic" mechanism, namely, intersystem crossing (ISC) along ultrafast internal conversion pathway electronically excited singlet species. For this purpose, we present a discussion ISC process and triplet-state reactivity based on theoretical analysis spin−orbit strength potential energy surfaces for relevant states cytosine. High-level ab initio computations show that is possible in wide regions manifold...

A review of direct dynamics methods is given, focusing on their application to non-adiabatic photochemistry–i.e. systems in which a conical intersection plays an important role. Direct simulations use electronic structure calculations obtain the potential energy surface only as it required 'on-the-fly'. This contrast traditional that require be globally known analytic function before simulation can performed. The properties and abilities, with descriptions made, three main are compared:...

Multiconfigurational ab initio calculations and QM/MM molecular dynamics simulations of a photoexcited cytosine−guanine base pair in both gas phase embedded the DNA provide detailed structural dynamical insights into ultrafast radiationless deactivation mechanism. Photon absorption promotes transfer proton from guanine to cytosine. This is followed by an efficient decay excited state via extended conical intersection seam. The optimization revealed that it has unusual topology, there only...

Knowledge about the electronic motion in molecules is essential for our understanding of chemical reactions and biological processes. The advent attosecond techniques opens up possibility to induce motion, observe it real time, potentially steer it. A fundamental question remains factors influencing decoherence role played by nuclear this process. Here, we simulate dynamics upon ionization polyatomic paraxylene modified bismethylene-adamantane, with a quantum mechanical treatment both...

Fixed-center Gaussian-type functions (GTF) have been used as basis sets in an extensive SCF–MO–CI study on H−, H2, and H3+. An accurate description requires 4 or 5 s-GTF each center, plus at least one set of p-GTF, which are essential for the reproduction reliable potential curves; d-GTF are, however, minor importance. A constant p exponent may be successfully a wide variety nuclear configurations. Variational energies − 1.3397 1.2765 hartree were calculated most stable equilateral collinear...

We report nonadiabatic dynamics computations on C2H4 + initiated a coherent superposition of the five lowest cationic states, employing Quantum Ehrenfest method. In addition to totally symmetric carbon-carbon double bond stretch and carbon-hydrogen stretches, we see that three non-totally modes become stimulated; torsion different CH stretching patterns. Thus, type involved in an attochemistry experiment, leads stimulation specific motions. The were also performed combination A C states....

CASSCF quantum chemical calculations (including dynamics) have been used to investigate the ultrafast photoisomerization of three symmetric cyanine dye models different chain lengths. For "model" trimethine cyanine, photochemical isomerization path can be divided into two phases: initial barrierless skeletal stretching coupled with torsional motion and decay process that takes place in region twisted intramolecular charge-transfer (TICT) minimum state an adjacent conical intersection. The is...