Approaching an exact treatment of electronic correlations at solid surfaces: The binding energy of the lowest bound state of helium adsorbed on MgO(100) (original) (raw)
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Periodic quantum mechanical simulation of the He-MgO(100) interaction potential
Chemical Physics, 2011
He-atom scattering is a well established and valuable tool for investigating surface structure. The correct interpretation of the experimental data requires an accurate description of the He-surface interaction potential. A quantum-mechanical treatment of the interaction potential is presented using the current dominant methodologies for computing ground state energies (Hartree-Fock, local and hybrid-exchange density functional theory) and also a novel post-Hartree-Fock ab initio technique for periodic systems (a local implementation of Møller-Plesset perturbation theory at second order). The predicted adsorption well depth and long range behavior of the interaction are compared with that deduced from experimental data in order to assess the accuracy of the interaction potential.
Adsorption energy and spin state of first-row transition metals adsorbed on MgO(100)
Physical Review B, 2003
Slab and cluster model spin-polarized calculations have been carried out to study various properties of isolated first-row transition metal atoms adsorbed on the anionic sites of the regular MgO͑100͒ surface. The calculated adsorption energies follow the trend of the metal cohesive energies, indicating that the changes in the metal-support and metal-metal interactions along the series are dominated by atomic properties. In all cases, except for Ni at the generalized gradient approximation level, the number of unpaired electron is maintained as in the isolated metal atom. The energy required to change the atomic state from high to low spin has been computed using the PW91 and B3LYP density-functional-theory-based methods. PW91 fails to predict the proper ground state of V and Ni, but the results for the isolated and adsorbed atom are consistent within the method. B3LYP properly predicts the ground state of all first-row transition atom the high-to low-spin transition considered is comparable to experiment. In all cases, the interaction with the surface results in a reduced high-to low-spin transition energy.
Surface Science, 1996
From periodic Hartree-Fock calculations, the mode of CO chemisorption on MgO(100) is found to vary with the coverage. At low coverage, the best adsorption mode is-predicted to be perpendicular to the surface. At higher coverages, the int~rdction between the adsorbed molecules influences the ordering of the surface. At coverage 0 = 1/2 monolayer, lateral effects dominate and CO is adsorbed paralle! to the surface, bridging pairs of nearest-neighbor Mg atoms. At 0 ffi 3/4, for the c(4 X 2) unit cell, the COs are adsorbed differently: whereas one third of the COs remains perpendicular to the surface, the two other thirds are bent on the surface. In this case, we find two geometrical arrangements that are equally favorable from an energetic standpoint. In a first arrangement, the non-perpendicular COs differ: one of them is tilted off-normal while the other one is parallel to the surface and bridges Mg atoms as at 0-I/2. This arrangement therefore distinguishes three kinds of COs. It is very close to results obtained by potential energy calculations. In another model, the two non-perpendicular COs are symmetrically positioned relative to the perpendicular one. This model distinguishes only two kinds of COs in a 2:1 ratio and is very close to results derived from spectroscopies at low temperature.
Surface core-level binding energy shifts for MgO(100)
Physical chemistry chemical physics : PCCP, 2014
Theoretical and experimental results for the surface core-level binding energy, BE, shifts, SCLS, for MgO(100) are presented and the anomalous O(1s) SCLS is interpreted in terms of the surface electronic structure. While the Mg(2p) surface BE shifts to a higher value than bulk by ≈1 eV as expected from the different surface and bulk Madelung potentials, the O(1s) SCLS is almost 0 rather than ≈-1 eV, expected from the Madelung potentials. The distortion of the surface atoms from the spherical symmetry of the bulk Mg and O atoms is examined by a novel theoretical procedure. The anomalous O SCLS is shown to arise from the increase of the effective size of surface O anions.
Physical Review B, 2011
The nature of the interaction of tris-(8-hydroxyquinoline) aluminum (Alq 3 ) with the Mg(001) surface is investigated by means of the van der Waals density functional. We show that there are strong chemical bonds between adsorbate O and substrate Mg atoms. The bonding energy is, however, canceled out by the energy required to distort the molecule and the surface upon adsorption. The van der Waals (vdW) interaction between the ligand and the surface stabilizes the chemisorption state. Our study clarifies the subtle interplay between covalent bonds, vdW attraction, and structural distortion.
Diffraction of helium on MgO(100) surface calculated from first-principles
Physical chemistry chemical physics : PCCP, 2014
In this work we simulate the diffraction peak intensities of He beams scattered on the MgO(100) surface from first principles. It turns out that diffraction peak intensities are extremely sensitive to the quality of the potential describing the He-MgO surface interaction. Achieving the required accuracy in first principles calculations is very challenging indeed. The present work describes a first principles protocol able to achieve very high accuracy for reasonable computational cost. This method is based on periodic local second-order Møller-Plesset perturbation theory where systematic corrections for basis set truncation and for high-order electronic correlation are introduced using coupled cluster calculations on finite model systems mimicking the target system. For the He-MgO system the requirements with respect to the level of theory are very high; it turns out that contributions from connected quadruple excitations are non-negligible. Here we demonstrate that using this proto...
Adsorption sites of individual metal atoms on ultrathin MgO(100) films
Physical Review B
We use Ca doping during growth of one-and two-monolayer-thick MgO films on Ag(100) to identify the adsorption sites of individual adatoms with scanning tunneling microscopy. For this we combine atomic resolution images of the bare MgO layer with images of the adsorbates and the substitutional Ca atoms taken at larger tip-sample distance. For Ho atoms, the adsorption sites depend on MgO thickness. On the monolayer, they are distributed on the O and bridge sites according to the abundance of those sites, 1/3 and 2/3, respectively. On the MgO bilayer, Ho atoms populate almost exclusively the O site. A third species adsorbed on Mg is predicted by density functional theory and can be created by atomic manipulation. Au atoms adsorb on the bridge sites for both MgO thicknesses, while Co and Fe atoms prefer the O sites, again for both thicknesses.
Spectroscopy of low-coordinated surface sites: Theoretical study of MgO
Physical Review B, 1999
We demonstrate a dramatic dependence on the oxygen coordination of the calculated optical absorption and luminescence energies of low-coordinated sites at the surfaces and in nanoclusters of MgO. The calculations for (MgO) 256 cubic nanoclusters were performed using an embedded molecular cluster model and both semiempirical and ab initio Hartree-Fock methods. The optical-absorption energies were calculated using the configuration interaction technique for single ͑CIS͒ and double electronic excitations. The luminescence energies were calculated using the CIS method. The low-coordinated sites included corners, kinks, step and cluster edges, and corner vacancy defects. We have also studied the zigzag steps and monatomic steps at infinite surfaces using a periodic density-functional theory method and a plane-wave basis set. For both the nanoclusters and infinite surfaces, the results show a consistent significant reduction of the exciton excitation energies and of the luminescence energies of relaxed excitons as the oxygen coordination decreases. We also demonstrate the possibility of exciton transfer from the sites with higher coordination to those with lower coordination and finally to the localization centers. Selective optical excitation of low-coordinated surface sites could be used to study molecular adsorption at surface sites, photocatalytic surface processes and desorption induced by electronic transitions.
Chemical Physics, 1992
The adsorption of isolated CO molecules on a perfect MgO(001) surface is investigated theoretically by the LCGTO-LDF cluster method. Internuclear distances, adsorption energies as well as frequencies and absolute intensities of the MgO-CO and C-O vibrational modes are calculated for a number of MgO/CO and MgO/OC model clusters containing 2-l 8 substrate atoms and a large array of surrounding point charges. The convergence of the computed observables with cluster size is discussed. The LDF results are compared to those of previous HF studies. MgO-CO adsorption is found to be mainly due to the electrostatic interaction of the CO molecule with the Madelung field on the surface. A small charge transfer of about 0.1 au from the CO 50 orbital to the substrate also takes place and, besides Pauli repulsion, contributes to the overall blue shift of the C-O vibrational frequency. The cluster models predict an approximate doubling of the C-O vibrational intensity upon adsorption. This intensity enhancement derives to a large extent from a change of the II: component of the CO dynamical dipole moment due to Pauli repulsion between the adsorbate at the cation atop position and the nearest neighbour surface anions. The calculated change of the C-O vibrational intensity is at variance with that obtained in a previous analysis of the observed coverage dependence of the C-O frequency. The MgO-CO vibrational mode is calculated to have a frequency lower than 200 cm-' and an absolute intensity of about 0.5 km/mol.