Visor de Contenidos

We have selected the following articles published in 2016:

1) The first selected article of our group presents an ab-initio study of the adsorption of noble gases on metallic surfaces, whic represents a paradigmatic case of van-der-Waals (vdW) interaction due to the role of screening effects on the corrugation of the interaction potential [J. L. F. Da Silva et al., Phys. Rev. Lett. 90, 066104 (2003)]. The extremely small adsorption energy of He atoms on the Mg(0001) surface (below 3 meV) and the delocalized nature and mobility of the surface electrons make the He/Mg(0001) system particularly challenging, even for state-of-the-art vdW-corrected density functional-based (vdW-DFT) approaches [M. P. de Lara-Castells et al., J. Chem. Phys. 143, 194701 (2015)]. In this work, we meet this challenge by applying two different procedures. First, the dispersion-corrected second-order Möller-Plesset perturbation theory (MP2C) approach is adopted, using bare metal clusters of increasing size. Second, the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)] is applied at coupled cluster singles and doubles and perturbative triples level, using embedded cluster models of the metal surface. Both approaches provide clear evidences of the anti-corrugation of the interaction potential: the He atom prefers on-top sites, instead of the expected hollow sites. This is interpreted as a signature of the screening of the He atom by the metal for the on-top configuration. The strong screening in the metal is clearly reflected in the relative contribution of successively deeper surface layers to the main dispersion contribution. Aimed to assist future dynamical simulations, a pairwise potential model for the He/surface interaction as a sum of effective He–Mg pair potentials is also presented, as an improvement of the approximation using isolated He–Mg pairs.

This study was developed in collaboration with Elena Voloshina from the Free University in Berlin.

María Pilar de Lara-Castells*Ricardo Fernández-Perea, Fani Fazharova, Elena Voloshina

Post-Hartree-Fock studies of the He/Mg(0001) interaction: Anti-corrugation, screening, and pairwise additivity

Journal of Chemical Physics, 2016, 144, 244707




2) The second selected paper presents an ab-initio study of the adsorbtion on noble gases on a titanium dioxide surface. It was developed within the framework of our collaboration with Akbar Salam from the Wake Forest University (USA). Weakly bound noble gases (Ne, Ar, Kr, and Xe) are being utilized as probes to monitor the photocatalytic activity of the TiO2(110) surface. In this work, this adsorption problem is examined using different van der Waals-corrected DFT-based treatments on periodic systems. The assessment of their performance is assisted by the application of nonperiodic DFT-based symmetry adapted perturbation theory [SAPT(DFT)]. It is further verified by comparing with experimentally based determinations of the adsorption energies at one-monolayer surface coverage. Besides being dispersion-dominated adsorbate/surface interactions, the SAPT(DFT)-based decomposition reveals that the electrostatic and induction energy contributions become highly relevant for the heaviest noble-gas atoms (krypton and xenon). The most reliable results are provided by the revPBE-D3 approach: it predicts adsorption energies of −118.4, −165.8, and −2231.7 meV for argon, krypton, and xenon, which are within 6% of the experimental values, and attractive long-range tails which are consistent with our ab initio benchmarking. Moreover, the revPBE density functional describes the short-range part of the potential energy curve more precisely, avoiding the exchange-only binding effects of the PBE functional. The nonlocal vdW-DF2 density functional performs well at the long-range potential region but largely overestimates the adsorption energies of noble gas atoms as light as argon. The Tkatchenko–Scheffler dispersion correction combined with the revPBE functional produces accurate estimations of the adsorption energies (to within 10%) but long-range attractive tails that decay too slowly as in first-generation nonlocal vdW-DF density functional. Lateral interactions between coadsorbate atoms contribute up to about 15–20%, being key in achieving good agreement with experimental measurements. The interaction with the noble-gas atoms reduces the work function of the TiO2(110) surface, agreeing to the experimental observation of an inhibited photodesorption of coadsorbed molecular oxygen.

A. A. Tamijani, A. Salam, María Pilar de Lara-Castells*

Adsorption of Noble-Gas Atoms on the TiO2(110) Surface: An Ab Initio-Assisted Study with van der Waals-Corrected DFT

Journal of Physical Chemistry C, 2016, 120, 18126-18139



3) The third selected publication presents a study of carbon nanotubes immersed in a superfluid helium nanodroplet. A recent experimental study [Ohba, Sci. Rep.2016, 6, 28992] of gas adsorption on single-walled carbon nanotubes at temperatures between 2 and 5 K reported a quenched propagation of helium through carbon nanotubes with diameters below 7 Å despite the small kinetic diameter of helium atoms. After assessing the performance of a potential model for the He–nanotube interaction via ab initio calculations with density functional theory-based symmetry adapted perturbation theory, we apply orbital-free helium density functional theory to show that the counterintuitive experimental result is a consequence of the exceptionally high zero-point energy of helium and its tendency to form spatially separated layers of helium upon adsorption at the lowest temperatures. Helium filling factors are derived for a series of carbon nanotubes and compared to the available experimental data.

This publication was led by Andreas W. Hauser (Graz University of Technology) and performed with the collaboration of María Pilar de Lara-Castells.

Andreas W. Hauser*, and María Pilar de Lara-Castells*

Carbon Nanotubes Immersed in Superfluid Helium: The Impact of Quantum Confinement on Wetting and Capillary Action

Journal of Physical Chemistry Letter, 2016, 7, 4929-4935.