Initio Calculations Of Potential Energy Curves Research Articles

Rydberg-State Double-Well Potentials of Van der Waals Molecules

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex ‘exotic’ structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted.

On the Viscosity and Physical Origin of Stability of Weakly Bound Complexes CdZn, HgZn and HgCd

Supermolecular CCSD(T)ab initiocalculations of potential energy curves for the electronic ground states of heteronuclear van der Waals complexes formed from the atoms of IIB group are presented. The physical origin of stability of the studied structures was analyzed by the symmetry-adapted perturbation theory. The magnitude of dispersion term increases with the increase of diatomic mass, but the relative importance of dispersion vs Hartree- Fock induction energies decreases in the order CdZn > HgZn > HgCd. Theoretical calculations of the temperature dependence of the shear viscosity for low-density binary mixtures are in good agreement with the temperature dependences of the shear viscosity obtained from empirical formula.

Ab initio calculation of transition dipole moments for transitions between valence states in oxygen molecules

Results of ab initio calculations of potential-energy curves for 20 singlet and 20 triplet valence states of oxygen with configuration interaction taken into account in the 6-31G basis are presented. Transition dipole moments of triplet-triplet (13Πg ← B3Σu−, 13Πg ← A3Σu+, 13Πg ← A′ 3Δu, B3Σ u− ← X3Σg−, 23Πu ← 13Π g, 23Σg− ← B3Σu−, 13Πu ← X3Σg−, 23Πu ← X3Σg−, 23Π g ← A′3Δu, 33Πg ← A′ 3Δ u, 23Δu ← 23Πg, 33Πg ← B3Σ u−, and 23Πg ← A3Σ u+) and singlet-singlet (21Σg+ ← 21Πu, 21Πu ← 11Π g, 1Πu ← 21Δg, 11Πg ← c1Σ u−, 1Πu ← b1Σg+, 11Δ u ← a1Δg, 21Πu ← a1Δg, 21Δg ← 11Δu, 1Π u ← a1Δ g, 11Πu ← b1Σg+, 21Πg ← 11Πu, 21Π g ← c1Σu−, 11Δ u ← 11Π g, f′Σ u+ ← b1Σg+, 21Σg+ ← f ′1Σ u+, 31Πg ← 11Δu) radiative transitions are calculated as functions of internuclear separation. The possibility of observing these transitions under experimental conditions is discussed.

Electron-energy-loss spectroscopy and ordered adsorbate layers on the Ni(100) surface

We have studied the lattice dynamics of ordered overlayers of adsorbate atoms on the (100) surface of an fcc crystal, with emphasis on contact with recent electron-energy-loss data on the $p(2\ifmmode\times\else\texttimes\fi{}2)$ and $c(2\ifmmode\times\else\texttimes\fi{}2)$ overlayers of oxygen on the Ni(100) surface. This is done within a model that fits the bulk phonon spectrum of Ni with nearest-neighbor centralforce couplings, and extracts adsorbate-substrate force constants from ab initio calculations of potential-energy curves carried out by Upton and Goddard. We obtain a very good fit to the data, but only if we assume the $c(2\ifmmode\times\else\texttimes\fi{}2)$ layer to be much closer to the surface than the $p(2\ifmmode\times\else\texttimes\fi{}2)$, as suggested by Upton and Goddard. We have also applied the model to ordered overlayers of sulfur on the Ni(100) surface, and we provide theoretical energy-loss spectra for this case. Throughout the discussion an emphasis is placed on features in the energy-loss spectrum which lie below the maximum phonon frequency of the substrate.