O. Roncero

An inversion technique for the calculation of embedding potentials

A new embedding method to include local correlation in large systems is proposed. In this method the density of the whole system, calculated via density functional theory approaches, is partitioned in two pieces, one corresponding to the subsystem of interest and the rest to the environment. In the second step, an embedding potential is obtained iteratively using as a driving force the self-repulsion due to the density difference, in a similar form as proposed by Zhao et al. [Phys. Rev. A 50, 2138 (1994)], to obtain the exact exchange-correlation functional. Such potential is added to the Fock equation to build the localized molecular orbitals which are further used to include the local electronic correlation in the subsystem of interest. This method is an alternative to the previous DFT-based embedding methods first proposed by Wesolowski and Washell [J. Phys. Chem. 97, 8050 (1993)] and after enhanced by Govind et al. [J. Chem. Phys. 110, 7677 (1999)] and adapted to metal extended systems, which use density functionals to describe the kinetic energy contribution to the embedding potential, whose precise form has been largely treated in the literature and its crucial role is discussed here. The method is applied to hydrogen chains and its van der Waals interaction with H(2). The results obtained are in very good agreement with exact calculations performed on the whole system, which demonstrates that the method proposed is a very promising route to introduce correlation in large systems.

A wave packet Golden Rule treatment of vibrational predissociation

The time‐dependent wave packet technique is applied to the Golden Rule treatment of vibrational predissociation. The wave packet at time zero is taken as the product of the quasibound wave function and the coupling inducing predissociation. The rate for vibrational predissociation can then be obtained by Fourier transform into the energy domain of the time‐dependent wave packet autocorrelation function. The method has been applied to a model triatomic van der Waals molecule. It is shown that when the bound‐state components of the wave packet are projected out, the time‐dependent version of the Golden Rule approximation provides an alternative efficient technique to treat intramolecular decay.

A new accurate and full dimensional potential energy surface of H5+ based on a triatomics-in-molecules analytic functional form

In this work a reliable full nine-dimensional potential energy surface for studying the dynamics of H(5)(+) is constructed, which is completely symmetric under any permutation of the nuclei. For this purpose, we develop a triatoms-in-molecules method as an extension of the more common diatoms-in-molecules one, which allows a very accurate description of the asymptotic regions by including correctly the charge-induced dipole and quadrupole interactions. Moreover, this treatment provides a semiquantitative description of all the topological features of the global potential compared with coupled cluster results. In particular, the hop of the proton between two H(2) fragments produces a double well in the potential. This resonant structure involving the five atoms produces a stabilization, lowering the barrier, and the triatoms-in-molecules yields to a barrier significantly higher than the ab initio results. Therefore, to improve the triatomics-in-molecules potential surface, two five-body terms are added, which are fitted to more than 110,000 coupled-cluster ab initio points. The global potential energy surface thus obtained in this work has an overall root mean square error of 0.079 kcal/mol for energies below 27 kcal/mol above the global well. The features of the potential are described and compared with previous available surfaces.

Nonradiative lifetimes for LiH in the A state using adiabatic and diabatic schemes

Accurate positions and nonradiative lifetimes of states belonging to the adiabatic A state of LiH are estimated. The results coming from a Golden Rule treatment in the adiabatic scheme present excellent agreement with those obtained through a diabatic close coupling calculation. That confirms the accuracy reached in both approaches and also in the treatment of the diabatic–adiabatic transformation. It involves, in particular, an effective phase control that is needed to properly estimate nonadiabatic couplings. Also, a powerful numerical procedure to obtain energy profiles in the diabatic close coupling frame is described and applied in this work.

On the orientation of molecular photofragments produced in highly excited rotational states

The degree of orientation of highly excited rotational states of molecular fragments produced by photodissociation with circularly polarized light is studied quantum mechanically. It is shown that a significant orientation of the fragments’ angular momentum j can be obtained when two or more dissociative continua correlated to the same final state of the products are excited simultaneously. In addition, the coherently excited continua should correspond to different helicity states, that is, to different projections of j on the reaction coordinate R (the vector joining the centers of mass of the fragments). The particular cases of an initial total angular momentum equal to zero as well as the axial recoil limit are discussed. The theory is applied to a simplified model of the photodissociation of ICN in the A continuum. The calculations have been performed by integration of the time independent quantum close‐coupling equations for the coupling between the rotation of CN and the reaction coordinate R, using...

Wave packet study of the Ne2I2 fragmentation dynamics: a four degrees of freedom model

Abstract We present a four degrees of freedom model that accounts for all possible fragmentation mechanisms in the vibrational predissociation of the Ne 2 I 2 van der Waals cluster. Calculations are performed by wave packet propagation and results are interpreted in terms of an analytical sequential model leading to a good agreement with experimental data.

Double continuum fragmentation in the vibrational predissociation X⋅⋅⋅BC(v)⋅⋅⋅Y→BC(v’<v)+X+Y of van der Waals complexes: A perturbative treatment

We present an approximate quantal model to study the double continuum problem arising in the complete fragmentation of X⋅⋅⋅BC(v)⋅⋅⋅Y van der Waals(vdW) complexes, where BC is a conventional diatomic molecule vibrationally excited and X and Y are rare gas atoms, through vibrational predissociation (VP). Assuming a near equilibrium geometry of the complex and using an adiabatic approximation for describing the oscillation in the angle formed by the BC⋅⋅⋅X and BC⋅⋅⋅Y weak bonds, the rates for complete fragmentation are expressed in the frame of Fermi’s ‘‘Golden Rule’’. Double continuum wave functions may be obtained by a perturbative treatment that allows one to take properly into account the symmetry of the problem in the particular and very frequent case X≡Y.

Time-dependent Hartree study of lifetimes for the Ne2I2 van der Waals cluster

Abstract The vibrational predissociation of the Ne2I2 van der Waals cluster is studied by a time-dependent Hartree type approach. Lifetimes for different initial vibrational states of I2 are computed and compared with the experimental results. The validity of this approach for studying vibrational predissociation is explored as well as the limitations and advantages.

Adsorption and nonadiabatic processes in the photodesorption of molecular oxygen from the reduced TiO2(110) surface

We review the adsorption and desorption of molecular oxygen on a reduced TiO 2 (110) surface. This system is known to play a fundamental role in heterogeneous photocatalysis. Periodic calculations are performed with the objec- tive of characterizing the variety of stable species of O 2 that are known to exist on the TiO 2 surface. The implications of our results for recent experiments are discussed. We also consider a direct optical excitation mechanism for the ultraviolet (UV) light-desorption process and model the most stable O 2 /TiO 2-x system as a cluster. High-level ab initio calculations of the excited states and interaction matrix elements are performed using different orbitals, separately optimized for the target states. The nonadiabatic and dipole-moment couplings are calculated directly from the corre- lated wave functions by a special transformation to bi-orthonormal (dual) orbital sets to preserve their structure. The method used for the electronic structure calculations is described in detail. Finally, the effect of the electronic coupling in the UV- photodesorption dynamics is analyzed in detail.

Application of a diabatic distorted wave approximation to the study of X⋅ ⋅ ⋅H2 (X=He, Ne, Ar) van der Waals molecules

A diabatic rotational decoupling scheme is applied to X⋅u2009⋅u2009⋅H2 van der Waals molecules using the anisotropic potentials of Tang and Toennies [J. Chem. Phys. 68, 5501 (1978); 74, 1148 (1981)]. We have developed the method proposed by Beswick and Requena [J. Chem. Phys. 72, 3018 (1980)] in an entirely numerical way. Attention is focused on the rotational predissociating levels and on the shape resonances of these systems. Among these resonances, a narrow orbiting and a narrow overbarrier resonances are found for the complexes Ne–H2 and Ar–H2, respectively. They should be amenable to experimental observation in molecular beam scattering as well as infrared spectroscopic studies.