Search results for "quantum theory"
showing 10 items of 234 documents
Impact of the synergistic collaboration of oligothiophene bridges and ruthenium complexes on the optical properties of dumbbell-shaped compounds.
2012
The linear and non-linear optical properties of a family of dumbbell-shaped dinuclear complexes, in which an oligothiophene chain with various numbers of rings (1, 3, and 6) acts as a bridge between two homoleptic tris(2,2'-bipyridine)ruthenium(II) complexes, have been fully investigated by using a range of spectroscopic techniques (absorption and luminescence, transient absorption, Raman, and non-linear absorption), together with density functional theory calculations. Our results shed light on the impact of the synergistic collaboration between the electronic structures of the two chemical moieties on the optical properties of these materials. Experiments on the linear optical properties …
Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes
2006
The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energ…
Communication: spin-orbit splittings in degenerate open-shell states via Mukherjee's multireference coupled-cluster theory: a measure for the couplin…
2012
We propose a generally applicable scheme for the computation of spin-orbit (SO) splittings in degenerate open-shell systems using multireference coupled-cluster (MRCC) theory. As a specific method, Mukherjee's version of MRCC (Mk-MRCC) in conjunction with an effective mean-field SO operator is adapted for this purpose. An expression for the SO splittings is derived and implemented using Mk-MRCC analytic derivative techniques. The computed SO splittings are found to be in satisfactory agreement with experimental data. Due to the symmetry properties of the SO operator, SO splittings can be considered a quality measure for the coupling between reference determinants in Jeziorski-Monkhorst base…
Quantum effects in the capture of charged particles by dipolar polarizable symmetric top molecules. II. Interplay between electrostatic and gyroscopi…
2013
ally nonadiabatic channel treatment of the capture of charged particles by dipolar polarizable symmetric top molecules with the aim to reveal quantum effects in the collision dynamics. In general, these effects are related to the discrete nature of the intrinsic, orbital, and total angular momenta, to the quantum character of passage of collision partners across effective potential barriers and drops, and to the interplay of two types of anisotropic interactions, the gyroscopic (Coriolis) and the electrostatic ones. The latter feature, in principle, leads to a coupling of capture channels. In the calculation of capture cross sections or rate coefficients, however, this coupling can be ignor…
Comparison of some dispersion-corrected and traditional functionals as applied to peptides and conformations of cyclohexane derivatives.
2012
We compare the energetic and structural properties of fully optimized α-helical and antiparallel β-sheet polyalanines and the energetic differences between axial and equatorial conformations of three cyclohexane derivatives (methyl, fluoro, and chloro) as calculated using several functionals designed to treat dispersion (B97-D, ωB97x-D, M06, M06L, and M06-2X) with other traditional functionals not specifically parametrized to treat dispersion (B3LYP, X3LYP, and PBE1PBE) and with experimental results. Those functionals developed to treat dispersion significantly overestimate interaction enthalpies of folding for the α-helix and predict unreasonable structures that contain Ramachandran φ and …
Post-Translational Regulation of CYP450s Metabolism As Revealed by All-Atoms Simulations of the Aromatase Enzyme.
2019
Phosphorylation by kinases enzymes is a widespread regulatory mechanism able of rapidly altering the function of target proteins. Among these are cytochrome P450s (CYP450), a superfamily of enzymes performing the oxidation of endogenous and exogenous substrates thanks to the electron supply of a redox partner. In spite of its pivotal role, the molecular mechanism by which phosphorylation modulates CYP450s metabolism remains elusive. Here by performing microsecond-long all-atom molecular dynamics simulations, we disclose how phosphorylation regulates estrogen biosynthesis, catalyzed by the Human Aromatase (HA) enzyme. Namely, we unprecedentedly propose that HA phosphorylation at Y361 markedl…
The chemistry of acetone at extreme conditions by density functional molecular dynamics simulations
2011
Density functional molecular dynamics simulations have been performed in the NVT ensemble (moles (N), volume (V) and temperature (T)) on a system formed by ten acetone molecules at a temperature of 2000 K and density ρ = 1.322 g cm(-3). These conditions resemble closely those realized at the interface of an acetone vapor bubble in the early stages of supercompression experiments and result in an average pressure of 5 GPa. Two relevant reactive events occur during the simulation: the condensation of two acetone molecules to give hexane-2,5-dione and dihydrogen and the isomerization to the enolic propen-2-ol form. The mechanisms of these events are discussed in detail.
Ab initio determination of the ionization potentials of DNA and RNA nucleobases
2006
Quantum chemical high level ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute vertical and adiabatic ionization potentials of the five canonical DNA and RNA nucleobases: uracil, thymine, cytosine, adenine, and guanine. Several states of their cations have been also calculated. The present results represent a systematic compendium of these magnitudes, establishing theoretical reference values at a level not reported before, calibrating computational strategies, and guiding the assignment of the features in the experimental photoelectron spectra. Daniel.Roca@uv.es Mercedes.Rubio@uv.es Manuela.Merchan@uv.es Luis.Serrano@uv.es
Quantum Games, Quantum States, Their Properties and Applications
2013
Elektroniskā versija nesatur pielikumus
Electronic fluxes during diels-alder reactions involving 1,2-benzoquinones: mechanistic insights from the analysis of electron localization function …
2012
By means of the joint use of electron localization function (ELF) and Thom's catastrophe theory, a theoretical analysis of the energy profile for the hetero-Diels-Alder reaction of 4-methoxy-1,2-benzoquinone 1 and methoxyethylene 2 has been carried out. The 12 different structural stability domains obtained by the bonding evolution theory have been identified as well as the bifurcation catastrophes (fold and cusp) responsible for the changes in the topology of the system. This analysis permits finding a relationship between the ELF topology and the evolution of the bond breaking/forming processes and electron pair rearrangements through the reaction progress in terms of the different ways o…