Search results for "UNESCO::FÍSICA::Química física"
showing 10 items of 81 documents
Method specific Cholesky decomposition : Coulomb and exchange energies
2008
We present a novel approach to the calculation of the Coulomb and exchange contributions to the total electronic energy in self consistent field and density functional theory. The numerical procedure is based on the Cholesky decomposition and involves decomposition of specific Hadamard product matrices that enter the energy expression. In this way, we determine an auxiliary basis and obtain a dramatic reduction in size as compared to the resolution of identity (RI) method. Although the auxiliary basis is determined from the energy expression, we have complete control of the errors in the gradient or Fock matrix. Another important advantage of this method specific Cholesky decomposition is t…
Rovibrational structure of the Ar–CO complex based on a novel three-dimensional ab initio potential
2002
The first three-dimensional ab initio intermolecular potential energy surface of the Ar–CO van der Waals complex is calculated using the coupled cluster singles and doubles including connected triples model and the augmented correlation-consistent polarized valence quadruple zeta (aug-cc-pVQZ) basis set extended with a (3s3p2d1f1g) set of midbond functions. The three-dimensional surface is averaged over the three lowest vibrational states of CO. Rovibrational energies are calculated up to 50 cm−1 above the ground state, thus enabling comprehensive comparison between theory and available experimental data as well as providing detailed guidance for future spectroscopic investigations of highe…
Study of the benzene⋅N2 intermolecular potential-energy surface
2003
The intermolecular potential-energy surface pertaining to the interaction between benzene and N2 is investigated theoretically and experimentally. Accurate intermolecular interaction energies are evaluated for the benzene–N2 van der Waals complex using the coupled cluster singles and doubles including connected triples [CCSD(T)] method and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. After fitting the energies to an analytic function, the intermolecular Schrödinger equation is solved to yield energies, rotational constants, and Raman-scattering coefficients for the lowest intermolecular levels of several benzene–N2 isotopomers. Experimentally, intermolecula…
Computational and experimental investigation of intermolecular states and forces in the benzene-helium van der Waals complex
2003
A study of the intermolecular potential-energy surface (IPS) and the intermolecular states of the perprotonated and perdeuterated benzene–He complex is reported. From a fit to ab initio data computed within the coupled cluster singles and doubles including connected triples model for 280 interaction geometries, an analytic IPS including two- to four-body atom–atom terms is obtained. This IPS, and two other Lennard-Jones atom–atom surfaces from the literature, are each employed in dynamically exact (within the rigid-monomer approximation) calculations of J = 0 intermolecular states of the isotopomers. Rotational constants and Raman-scattering coefficients for intermolecular vibrational trans…
Multiconfigurational second-order perturbation study of the decomposition of the radical anion of nitromethane
2004
The doublet potential energy surfaces involved in the decomposition of the nitromethane radical anion (CH(3)NO(2) (-)) have been studied by using the multistate extension of the multiconfigurational second-order perturbation method (MS-CASPT2) in conjunction with large atomic natural orbital-type basis sets. A very low energy barrier is found for the decomposition reaction: CH(3)NO(2) (-)--[CH(3)NO(2)](-)--CH(3)+NO(2) (-). No evidence has been obtained on the existence of an isomerization channel leading to the initial formation of the methylnitrite anion (CH(3)ONO(-)) which, in a subsequent reaction, would yield nitric oxide (NO). In contrast, it is suggested that NO is formed through the …
Current density maps, magnetizability, and nuclear magnetic shielding tensors of bis-heteropentalenes. II. Furo-furan Isomers
2004
Magnetic susceptibility and nuclear magnetic shielding at the nuclei of bis-heteropentalenes formed by two furan units ([2,3-b], [3,2-b], [3,4-b], and [3,4-c] isomers) have been computed by several approximated techniques and a large Gaussian basis set to achieve near Hartree–Fock estimates. Ab initio models of the ring currents induced by a magnetic field normal to the molecular plane were obtained for the three isomeric systems of higher symmetry, showing that the π electrons give rise to intense diamagnetic circulation. The π currents are responsible for enhanced magnetic anisotropy and strong out-of-plane proton deshielding. The theoretical findings are used to build up a “diatropicity …
Oxamate-containing palladium(II) complexes: an open gate in fundamental and applied chemistry
2015
La versatilidad que ofrece el ligando oxamato funcionalizado con distintos sustituyentes en forma aniónica, ha permitido desarrollar una química de coordinación muy extensa y variada. Sus inicios datan de los años ochenta, a cargo del Profesor O. Kahn y colaboradores, con una atención particular en estudios de propiedades magnéticas y estructuras cristalinas. La continuación y profundización de dicha química, desde la perspectiva del magnetismo molecular, es una línea de trabajo que nuestro grupo de investigación viene desarrollando en el ICMol durante las últimas dos décadas. Su mayor interés radica en la obtención de oxamato complejos multifuncionales. En esa Tesis Doctoral, hemos tratado…
Química Física avanzada (2009/2010)
2009
La asignatura Química Física Avanzada es una asignatura troncal de carácter anual. En el plan de estudios actualmente en vigor consta de un total de 9.0 créditos ECTS.
Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4-(dimethylamino)benzonitrile?
2009
International audience; We present here the results of time-resolved absorption and emission experiments for 4-(dimethylamino)benzonitrile in solution, which suggest that the fluorescent intramolecular charge transfer (ICT) state may differ from the twisted ICT (TICT) state observed in transient absorption.
Nanomateriales basados en lantánidos: caracterización y visualización
2022
Las nanopartículas upconversion (UCNP) comenzaron a desarrollarse a inicios del presente siglo, generando una gran expectación e interés por sus propiedades fotofísicas particulares. Las UCNP son nanomateriales capaces de producir el fenómeno upconversion (UC) mediante el cual fotones de baja energía (de la región del infrarrojo cercano, NIR) se transforman en fotones de alta energía (en la región del UV-vis). Los principales actores del fenómeno son los iones lantánidos que se encuentran como dopantes de una matriz nanométrica transparente. Por tanto, en las UCNP, a diferencia de las nanopartículas (NP) semiconductoras, el confinamiento nanométrico no es el responsable de las propiedades ó…