Stability conditions for the solutions of the Half-Projected Hartree-Fock scheme. The lithium-hydride ground state

4 págs.; 1 fig.; 2 tabs.The stability conditions for the solutions of a two-unrestricted-determinant function (the half-projected Hartree-Fock function) are deduced from the necessary requirements for the minimization of the energy functional. The theory is applied to the case of the LiH ground state, in order to investigate the various solutions encountered in the variational problem. It is found that the two lowest solutions are local minima. The number of these solutions is estimated and their significance discussed as a function of the nuclear separation. © 1977 The American Physical Society.Peer Reviewe

Estudio de la correlación electrónica en aproximaciones de capas desdobladas : aplicación al hidruro de litio

Tesis inédita de la Universidad de Madrid, Facultad de Ciencias, Sección de Químicas, leída el 23 de mayo de 1973.Universidad de MadridTRUEProQuestpu

Spectral simulations and vibrational dynamics of the fluxional H+5 cationand its isotopologues: signatures of the shared-proton motions

1 pag.; 2 figs. PACS 33.20.Tp Vibrational analysis; 34.50.-s Scattering of atoms and molecules; 31.15.-p Calculations and mathematical techniques in atomic and molecular physics; 33.15.Mt Rotation, vibration, and vibration-rotation constants. XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013) IOP Publishing.The recent increased interest on research studies of the H+5 cation, and its isotopologues, is due to the postulation for their presence, although still not detected, in the interstellar medium. There is no doubt, particularly in the light of the recent laboratory observations, that the spectroscopy of these systems is also a great challenge for the theorists. Thus, we report the first fully converged coupled anharmonic quantum study on vibrational dynamics of these highly fluxional cations, providing important information on their spectroscopy in a rigorous manner, and open perspectives for further investigations. Published under licence by IOP Publishing LtdPeer Reviewe

Ab initio ground state potential energy surfaces for Rg–Br2 (Rg = He, Ne, Ar) complexes

6 pages, 3 figures, 5 tables.-- PACS: 31.15.Ar; 31.15.Dv; 33.15.Bh; 33.15.MtHigh-level ab initio molecular electronic structure calculations are performed for Rg–Br2 (Rg = He, Ne, Ar) complexes at CCSD(T) (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) level of theory. Specific augmented correlation consistent basis sets are used for each noble atom (Rg), supplemented with an additional set of bond functions. Effective-core potentials (ECPs), augmented with diffusion (sp) and polarization (3df ) functions, have been employed for the bromine atoms. For all complexes, the CCSD(T) potential energy surfaces (PESs) show double-minimum topology, with wells at both linear and T-shaped configurations; the linear minimum is found to be deeper than the T-shaped one. Vibrational corrections are taken into account for all the complexes and their effects in the stability of the linear and T-shaped conformers are examined. For each complex and each configuration (linear and T-shaped), Re equilibrium intermolecular distances, De and D0 dissociation energies, are evaluated and compared with previous theoretical and/or experimental results.This work has been supported by DGICYT, Spain, Grant No. BCM 2001-2179 and by a European TMR network, Grant No. HPRN-CT-1999-00005. C.C. is indebted to CNPq, Brazil for supporting his postdoctoral at C.S.I.C, Proc. 200688/ 00-6 and R.P. acknowledges a postdoctoral fellowship by MEC, Spain, Ref. No. SB99 N0714831.Peer reviewe

Potential energy surface and spectroscopy of clusters of rare-gas atoms with cyclopropane

Analytical empirical potential energy surfaces describing the van der Waals interaction between rare-gas atoms and cyclopropane are presented. The functional form is based on pairwise Lennard-Jones-type potentials which have been widely used to describe rare-gas-benzene complexes, also studied in this work in order to check our theoretical method and for comparison. The parameters have been chosen in order to accurately fit the high resolution microwave spectra recently reported by Xu and Jäger [J. Chem. Phys. 106, 7968 (1997)]. The observed splitting in the microwave spectra of Ne-cyclopropane, associated with rotational tunneling, is well reproduced. Moreover, such tunneling is also important for complexes of Ar and Kr in excited van der Waals states. These phenomena involve a high delocalization of the wave functions and, therefore, intermolecular spectroscopy techniques would provide a good check of the potential energy surface over a broad region of the configuration space. © 1998 American Institute of Physics.This work has been supported by Consejería de Educación, Cultura y Deportes del Gobierno de Canarias under Grant No. PI 2/95, DGYCIT (Spain) under Grant No. PB95- 0071, and by the European TMR network Contract No. ERBFMRX-CT96-0088.Peer Reviewe

Frequency domain description of Kohlrausch response through a pair of Havriliak-Negami-type functions: An analysis of functional proximity

An approximation to the Fourier transform (FT) of the Kohlrausch function (stretched exponential) with shape parameter 0<β≤1 is presented by using Havriliak-Negami-like functions. Mathematical expressions to fit their parameters α, γ, and τ, as functions of β (0<β≤1 and 1<β<2) are given, which allows a quick identification in the frequency domain of the corresponding shape factor β. Reconstruction via fast Fourier transform of frequency approximants to time domain are shown as good substitutes in short times though biased in long ones (increasing discrepancies as β→1). The method is proposed as a template to commute time and frequency domains when analyzing complex data. Such a strategy facilitates intensive algorithmic search of parameters while adjusting the data of one or several Kohlrausch-Williams-Watts relaxations. © 2011 American Physical Society.This work has been supported by DGICYT, Spain, Grant No. FIS2010-18132.Peer Reviewe

Ab initio vibrational predissociation dynamics of He-I2(B) complex

7 pages, 5 figures, 5 tables.-- PACS nrs.: 31.15.Ar; 31.15.Dv; 33.80.Gj; 33.20.Tp; 33.70.Ca.Three-dimensional quantum mechanical calculations on the vibrational predissociation dynamics of HeI2 B state complex are performed using a potential energy surface accurately fitted to unrestricted open-shell coupled cluster ab initio data, further enabling extrapolation for large I2 bond lengths. A Lanczos iterative method with an optimized complex absorbing potential is used to determine energies and lifetimes of the vibrationally predissociating He,I2(B,v') complex for v' ≤ 26 of I2 vibrational excitations. The calculated predissociating state energies agree with recent experimental results within 0.5 cm−1. This excellent agreement is remarkable since no adjustment was made with respect to the experiments. The present ab initio approach, however, shows its limitations in the fact that the computed lifetimes that are highly sensitive to subtle details of the potential energy surfaces such as anisotropy, are a factor of 1.5 larger than the available experimental data.The Centro de Cálculo (IMAFF), CTI (CSIC), CESGA, and MareNostrum (BSC) are acknowledged for allocation of computer time. One of the authors (A.V.) would like to thank CICYT, Spain for a grant to support his stay at the Laboratoire Collisions, Agrégats, Réactivité. One of the authors (R.P.) acknowledges support by Ramón y Cajal Programme Grant No. PDRYC-2006-001017. This work has been supported by DGICYT, Spain, Grant No. FIS2004-02461 and CSIC-CNRS, Grant No. 2005-FR0031.Peer reviewe

An optimized full-configuration-interaction nuclear orbital approach to a “hard-core” interaction problem: Application to (3He)N–Cl2(B) clusters (N<4)

13 pages, 8 figures, 3 tables, 3 appendix.An efficient full-configuration-interaction nuclear orbital treatment has been recently developed as a benchmark quantum-chemistry-like method to calculate ground and excited “solvent” energies and wave functions in small doped AEest clusters (N<4) [M. P. de Lara-Castells, G. Delgado-Barrio, P. Villarreal, and A. O. Mitrushchenkov, J. Chem. Phys. 125, 221101 (2006)]. Additional methodological and computational details of the implementation, which uses an iterative Jacobi–Davidson diagonalization algorithm to properly address the inherent “hard-core” He–He interaction problem, are described here. The convergence of total energies, average pair He–He interaction energies, and relevant one- and two-body properties upon increasing the angular part of the one-particle basis set (expanded in spherical harmonics) has been analyzed, considering Cl2 as the dopant and a semiempirical model (T-shaped) He–Cl2(B) potential. Converged results are used to analyze global energetic and structural aspects as well as the configuration makeup of the wave functions, associated with the ground and low-lying “solvent” excited states. Our study reveals that besides the fermionic nature of 3He atoms, key roles in determining total binding energies and wave-function structures are played by the strong repulsive core of the He–He potential as well as its very weak attractive region, the most stable arrangement somehow departing from the one of N He atoms equally spaced on equatorial “ring” around the dopant. The present results for N=4 fermions indicates the structural “pairing” of two 3He atoms at opposite sides on a broad “belt” around the dopant, executing a sort of asymmetric umbrella motion. This pairing is a compromise between maximizing the 3He–3He and the He-dopant attractions, and suppressing at the same time the “hard-core” repulsion. Although the He–He attractive interaction is rather weak, its contribution to the total energy is found to scale as a power of three and it thus increasingly affects the pair density distributions as the cluster grows in size.This work has been partially supported by the CSICCAM, CICYT, and MICINN-CSIC Spanish Grants Nos. CCG08-CSIC/ESP-3680, FIS2007-62006, and 2007501004.Peer reviewe

Competitive internal transfers in metastable decay of cluster ions

In a previous study of fragmentation patterns of (Ar)3 + clusters [G. Delgado-Barrio, S. Miret-Artés, P. Villarreal, and F. A. Gianturco, Z. Phys. D 27, 354 (1993)] it was found that overall rotations control the lifetimes of the occupied metastable states of the cluster and that a spherical, effective interaction was sufficient to describe the dynamical process. In the present study, the strong anisotropy of a more realistic three-particle interaction is introduced and its effects on metastable decay are examined. By separating internal rotations from internal vibrations of the diatomic ion, it is possible to show that internal predissociation pathways are very efficient and lead to very short lifetimes. The latter can be lengthened only when overall rotational states are directly included, thus confirming the physical picture of the earlier work. © 1994 American Institute of Physics.The financial funding of the computing time by the Italian National Research Council (CNR) is also acknowledged.Peer Reviewe