Institute Fsica Fundamental IFF CSIC

Serrano, Spain

Institute Fsica Fundamental IFF CSIC

Serrano, Spain
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Valdes A.,Institute Fsica Fundamental IFF CSIC | Prosmiti R.,Institute Fsica Fundamental IFF CSIC | Villarreal P.,Institute Fsica Fundamental IFF CSIC | Delgado-Barrio G.,Institute Fsica Fundamental IFF CSIC
Journal of Chemical Physics | Year: 2011

Benchmark, full-dimensional calculations on the ground and excited vibrational states for the tetra-, and penta-atomic weakly bound He 2,3ICl complexes are reported. The representation of the potential energy surfaces includes three-body HeICl potentials parameterized to coupled-cluster singles, doubles, and perturbative triples ab initio data. These terms are important in accurately describing the interactions of such highly floppy systems. The corresponding 6D/9D computations are performed with the multi-configuration time dependent Hartree method, using natural potential fits, and a mode combination scheme to optimize the computational effort in the improved relaxation calculations. For these complexes several low-lying vibrational states are computed, and their binding energies and radial/angular probability density distributions are obtained. We found various isomers which are assigned to different structural models related with combinations of the triatomic isomers, like linear, T-shaped, and antilinear ones. Comparison of these results with recent experimental data is presented, and the quantitative deviations found with respect to the experiment are discussed. © 2011 American Institute of Physics.


Valdes L.,Institute Fsica Fundamental IFF CSIC | Prosmiti R.,Institute Fsica Fundamental IFF CSIC | Villarreal P.,Institute Fsica Fundamental IFF CSIC | Delgado-Barrio G.,Institute Fsica Fundamental IFF CSIC
Journal of Chemical Physics | Year: 2011

Quantum dynamics calculations are reported for the tetra-, and penta-atomic van der Waals HeNBr2 complexes using the multiconfiguration time-dependent Hartree (MCTDH) method. The computations are carried out in satellite coordinates, and the kinetic energy operator in this set of coordinates is given. A scheme for the representation of the potential energy surface based on the sum of the three-body HeBr2 interactions at CSSD(T) level plus the He-He interaction is employed. The potential surfaces show multiple close lying minima, and a quantum description of such highly floppy multiminima systems is presented. Benchmark, full-dimensional converged results on ground vibrational/zero-point energies are reported and compared with recent experimental data available for all these complexes, as well as with previous variational quantum calculations for the smaller HeBr2 and He2Br2 complexes on the same surface. Some low-lying vibrationally excited eigenstates are also computed by block improved relaxation calculations. The binding energies and the corresponding vibrationally averaged structures are determined for different conformers of these complexes. Their relative stability is discussed, and contributes to evaluate the importance of the multiple-minima topology of the underlying potential surface. © 2011 American Institute of Physics.


Valdes A.,Institute Fsica Fundamental IFF CSIC | Prosmiti R.,Institute Fsica Fundamental IFF CSIC
Journal of Physical Chemistry A | Year: 2013

Reduced dimensional quantum dynamics calculations of the infrared spectrum of the H5 + and D5 + clusters are reported in both low, 300-2200 cm-1, and high, 2400-4500 cm -1, energy regions. The proposed four-dimensional quantum model describes the motion of the proton between the two vibrating hydrogen molecules. The simulations are performed using time-dependent and time-independent approaches within the multiconfiguration time-dependent Hartree method. Propagation of the wavepackets includes an absorbing scheme to deal with vibrational dissociating states, and to assign the different spectral lines, block improved relaxation computations are performed for both bound and predissociative vibrational states of the systems. The reported computations make use of an analytical ab initio-based potential energy, and "on the fly" DFT dipole moment surfaces. The predominant features in the spectra are assigned to the excitations of the shared-proton stretch mode, and above dissociation the symmetric and antisymmetric stretching of the two H2 and the breathing mode of H3 + are also involved. The computed infrared absorption spectra for both cations are in very good agreement with the recent experimental measurements available from multiple-photon dissociation and mass-selected single-photon photodissociation spectroscopy techniques. Comparison of the present results with previous theoretical calculations on these systems is also presented. Such comparisons between different theoretical approaches and experimental measurements can serve to evaluate the approximations employed, and to guide higher-order computations. © 2013 American Chemical Society.

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