152 research outputs found
Electron correlation effects in diamond: a wave-function quantum chemistry study of the quasiparticle band structure
The quasiparticle bands of diamond, a prototype covalent insulator, are
herein studied by means of wave-function electronic-structure theory, with
emphasis on the nature of the correlation hole around a bare particle.
Short-range correlations are in such a system conveniently described by using a
real-space representation and many-body techniques from {\it ab initio} quantum
chemistry. To account for long-range polarization effects, on the other hand,
we adopt the approximation of a dielectric continuum. Having as "uncorrelated"
reference the Hartree-Fock band structure, the post-Hartree-Fock treatment is
carried out in terms of localized Wannier functions derived from the
Hartree-Fock solution. The computed correlation-induced corrections to the
relevant real-space matrix elements are important and give rise to a strong
reduction, in the range of , of the initial Hartree-Fock gap. While our
final results for the indirect and direct gaps, 5.4 and 6.9 eV, respectively,
compare very well with the experimental data, the width of the valence band
comes out by to too large as compared to experiment. This
overestimation of the valence-band width appears to be related to
size-consistency effects in the configuration-interaction correlation
treatment.Comment: 16 pages, 7 figures, accepted at Phys. Rev. B (2014
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
Accurate <i>ab initio</i> ro-vibronic spectroscopy of the X<sup>2</sup>∏ CCN radical using explicitly correlated methods
Explicitly correlated CCSD(T)-F12b calculations have been carried out with systematic sequences of correlation consistent basis sets to determine accurate near-equilibrium potential energy surfaces for the X<sup>2</sup>∏ and a<sup>4</sup>Σ<sup>−</sup> electronic states of the CCN radical. After including contributions due to core correlation, scalar relativity, and higher order electron correlation effects, the latter utilizing large-scale multireference configuration interaction calculations, the resulting surfaces were employed in variational calculations of the ro-vibronic spectra. These calculations also included the use of accurate spin-orbit and dipole moment matrix elements. The resulting ro-vibronic transition energies, including the Renner-Teller sub-bands involving the bending mode, agree with the available experimental data to within 3 cm<sup>−1</sup> in all cases. Full sets of spectroscopic constants are reported using the usual second-order perturbation theory expressions. Integrated absorption intensities are given for a number of selected vibronic band origins. A computational procedure similar to that used in the determination of the potential energy functions was also utilized to predict the formation enthalpy of CCN, ΔH<sub>f</sub>(0K) = 161.7 ± 0.5 kcal/mol
Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods
In existing theoretical approaches to core-level excitations of
transition-metal ions in solids relaxation and polarization effects due to the
inner core hole are often ignored or described phenomenologically. Here we set
up an ab initio computational scheme that explicitly accounts for such physics
in the calculation of x-ray absorption and resonant inelastic x-ray scattering
spectra. Good agreement is found with experimental transition-metal -edge
data for the strongly correlated cuprate LiCuO, for which we
determine the absolute scattering intensities. The newly developed methodology
opens the way for the investigation of even more complex electronic
structures of group VI B to VIII B correlated oxide compounds
Physisorption of helium on a TiO2(110) surface: periodic and finite clusters approaches
Workshop CMST Action CM1200 CODECS: Holistic Computational Spectroscopy, 16-18 November 2011, Pisa, Italy. http://codecs.sns.it/index.php/Holistic_Computational_SpectroscopyAs a proto-typical case of physisorption on an extended transition-metal oxide surface, the interaction of a helium atom with a TiO2(110) surface is studied here by using finite cluster and periodic approaches and both wavefunction-based (post Hartree-Fock) quantum chemistry methods, as well as density functional theory. The finite cluster approach is applied to provide reference results at coupled-cluster and perturbative second-order Möller-Plesset levels of theory. It is shown that once the basis set is specifically tailored to minimize the basis set superposition error, periodic calculations using the Perdew Burke-Ernzerhof functional yield short and medium-range interaction potentials in very reasonable agreement with those obtained using the correlated wave-function-based methods, while small long-range dispersion corrections are necessary to reproduce the correct asymptotic behavior. This study is aimed at the simulation of helium droplet-mediated deposition of metallic clusters on oxide surfaces.Peer Reviewe
Communication: A combined periodic density functional and incremental wave-function-based approach for the dispersion-accounting time-resolved dynamics of 4He nanodroplets on surfaces: 4He/graphene
Helium mediated deposition: Modeling the He−TiO2(110)-(1×1) interaction potential and application to the collision of a helium droplet from density functional calculations
This paper is the first of a two-part series dealing with quantum-mechanical (density-functional-based) studies of helium-mediated deposition of catalytic species on the rutile TiO2(110)-(1×1) surface. The interaction of helium with the TiO2(110)-(1×1) surface is first evaluated using the Perdew-Burke-Ernzerhof functional at a numerical grid dense enough to build an analytical three-dimensional potential energy surface. Three (two prototype) potential models for the He-surface interaction in helium scattering calculations are analyzed to build the analytical potential energy surface: (1) the hard-corrugated-wall potential model; (2) the corrugated-Morse potential model; and (3) the three-dimensional Morse potential model. Different model potentials are then used to study the dynamics upon collision of a 4He300 cluster with the TiO2(110) surface at zero temperature within the framework of a time-dependent density-functional approach for the quantum fluid [D. Mateo, D. Jin, M. Barranco, and M. Pi, J. Chem. Phys. 134, 044507 (2011)] and classical dynamics calculations. The laterally averaged density functional theory-based potential with an added long-range dispersion interaction term is further applied. At variance with classical dynamics calculations, showing helium droplet splashing out of the surface at impact, the time evolution of the macroscopic helium wave-function predicts that the helium droplet spreads on the rutile surface and leads to the formation of a thin film above the substrate. This work thus provides a basis for simulating helium mediated deposition of metallic clusters embedded within helium nanodroplets
ExoMol line lists – LI. Molecular line lists for lithium hydroxide (LiOH)
New molecular line lists for lithium hydroxide (6Li16O1H and 7Li16O1H isotopologues) covering wavelengths λ > 1 μ
m (0–10 000 cm−1 range) are presented. Each line list contains around 300 million transitions between rotation–vibration energy levels with total angular momentum up to J = 95, applicable for temperatures up to T ≈ 3500 K. Line list calculations were based on a previously published, high-level ab initio potential energy surface and a newly computed dipole moment surface of the ground X~1Σ+
electronic state. Lithium-containing molecules are important in a variety of stellar objects and there is potential for LiOH to be observed in the atmospheres of exoplanets. Transit spectra are simulated using the rocky super-Earth 55 Cancri e as an example with two different atmospheric scenarios including LiOH. This work provides the first, comprehensive line lists of LiOH to facilitate its future molecular detection. The OYT7 line lists along with the associated temperature- and pressure-dependent molecular opacities can be downloaded from the ExoMol database at www.exomol.com and the CDS astronomical database
A Combined Periodic Density Functional and Incremental Wave-Function-Based Approach for the Dipersion-Accounting Time-Resolved Dynamics of 4He Nanodroplets on Surfaces: 4He/Graphene
Helium-mediated Synthesis, Soft-landing and Spectroscopy of Metal Nanoparticles on Surfaces,CSIC, Madrid, Spain, October 10-11, 2014A general strategy to calculate accurate He-surface interaction potentials is proposed [1]. It extends the dispersionless density functional (dlDF) approach by Pernal et al. [2] to adsorbatesurface interactions by including periodic boundary conditions [1b]. A scheme to parametrize the dispersion interaction is introducced by calculating two- and three-body dispersion terms at CCSD(T) level via the method of increments [3]. The performance of the composite approach is tested on the low-lying selective adsorption states of 4He/graphene [5]. Second, its capability to describe dispersionless correlation effects realistically is used to extract dispersion effects in time-dependent density functional simulations on the collision of 4He droplets with graphene [1b]. Dispersion effects play a key role in the fast spreading of the 4He nanodroplet [1b,6], the evaporation-like process of helium atoms, and the formation of solid-like helium structures. These characteristics are expected to be quite general and highly relevant to explain experimental measurements with the newly developed helium droplet mediated deposition technique [7].Peer Reviewe
ExoMol line lists -- LI. Molecular line list for lithium hydroxide (LiOH)
A new molecular line list for lithium hydroxide (LiOH)
covering wavelengths m (the 0-10000 cm range) is
presented. The OYT7 line list contains over 331 million transitions between
rotation-vibration energy levels with total angular momentum up to and
is applicable for temperatures up to K. Line list calculations
are based on a previously published, high-level \textit{ab initio} potential
energy surface and a newly computed dipole moment surface of the ground
\tilde{X}\,^1\Sigma^+ electronic state. Lithium-containing molecules are
important in a variety of stellar objects and there is potential for LiOH to be
observed in the atmospheres of exoplanets. This work provides the first,
comprehensive line list of LiOH and will facilitate its future molecular
detection. The OYT7 line list along with the associated temperature- and
pressure-dependent opacities can be downloaded from the ExoMol database at
www.exomol.com and the CDS astronomical database
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