Rare gases dimers

Patton, D. C., Pederson, M. R., 1997, Application of the Generalized-Gradient Approximation to Rare-Gas Dimers , Phys. Rev. A, 56, R2495. 

In the following section, we will reexamine some earlier recombination measurements to see if third-body effects may have played a role. The rare gas dimer ions provide a good starting point. 

The various observations leave little doubt that recombination of rare-gas dimer ions can produce excited atoms, but it is quite possible that formation of radiating excited states occurs only in a small fraction of recombination events. If this is true, then the observed line shapes do not reflect the dominant recombination mecha-... 

Tao J, Perdew JP (2005) Test of a nonempirical density functional Short-range part of the van der Waals interaction in rare-gas dimers, J Chem Phys, 122 11402... 

One of the most commonly employed procedures has been to simply extrapolate the molecular coupling from the available atomic parameters using the so-called atoms-in-molecules approach (72). Here (r,) is assumed to be constant for electrons with the same n and / quantum numbers. The values of are then assumed to be equal to the spin-orbit coupling constants n/, which are derived from atomic spectral data. This approach has been employed by Wadt (73) in all-electron studies, and by other groups (32,74) in effective potential calculations involving the rare-gas dimers and dimer ions. Ermler and co-workers used this approach coupled with AREP calculations to determine spectroscopic properties for various states of Au2 (42), Hg2, and HgTl (75). 

If we want to predict the structure, the stability and the vibrational and rotational spectra of Van der Waals molecules, we have to know the complete intermolecular potential as a function of the intermolecular distanoe(s) and the molecular orientations. For rare gas dimers and for some rare gas atom-diatomic molecule (e.g. 

The latter systems have only two internal degrees of freedom, however, (in the rigid molecule approximation) and the rare gas dimers have just a single one, of course. Some ab initio studies have been made of molecular Van der Waals (or hydrogen bonded) systems with more internal coordinates but mostly they concern only specific points or one-dimensional cuts (e.g. distance curves for fixed molecular orientations) of the potential (hyper) surface. One exception is the case of the simplest molecular dimer (112)2, which has been studied in detail, both ab and experimentally Another exception form the two Van der Waals molecules, (C2H and ( 2)2, of which the complete potential surfaces have been obtained in our institute via ab initio calculations. The N2—N2 potential, in particular, has been the subject of much previous (s ni-) empirical work . The dimers (N2)2 and (C2HJ2 have been investi-... 

Photoionization studies of rare gas dimers have been carried out . Photoionization efficiency curves for the vdW molecules (Ar. .. Ar, Kr. .. Kr, Xe. .. Xe) were obtained by means of molecular beam techniques. The dissociation energies of the ions were calculated from the measured first ionization potentials (Table 6) and the dissociation energies of the parent vdW molecules. As the dissociation energy of vdW molecules is neghgible compared the dissociation energy of the rresponding cations, the latter energies (available from other sources) can be used to estimate first ionization potentials of vdW systems which have not yet been studied (values in parentheses in Table 6). 

Analysis of photon yield curves of rare gas dimers has shown that the main mechanism participating in photoionization is autoionization ... 

Table 6. First ionization potential of vdW molecules Rare gas dimers. For comparison are induded also potentials for atoms (Ref. unless otherwise stated)...

In the zeroth order (the first six terms in Eq. 94), the sum of the exchange-correlation and functionals AExc[p] + ATs p] is calculated the same electron density (Pa + p%, P°a, or p°B). Therefore, the zeroth-order contribution to the error of the calculated interaction energy depends on the sum of errors of these two functionals. Any cancellation of errors in Ts[p] and Exc[p] results thus in improvement in the calculated interaction energies. The remarkably good accuracy of the KSCED(LDA) interaction energies for rare-gas dimers can be seen as an illustration that such cancellation takes place at the LDA level. The zeroth-order terms are dominant not only for rare-gas dimers. Table 5 shows that it amounts to more than 95% of the interaction energy for complexes formed by small hydrocarbon molecules. Even for complexes formed by carbazole and Ne, Ar, N2, CO, and CH4 molecules zeroth-order contributions amount to about (80-90%) of the KSCED interaction energy108. 

Examination and Parameterization of Interatomic Potentials for Rare Gas Dimers I 131... 

Rare gas dimers are prototypical systems to examine van der Waals interaction function forms [88, 92, 98-100]. It should be noted that such examinations on the vdW potentials generally employ the assumption that the total interactions between two rare gas atoms are all from the vdW interactions. A seminal work by Halgren [88] found that neither the Lennard-Jones type potentials (Lennard-Jones 12-6 or Lennard-Jones 9-6) nor the Buckingham exp-6 potentials was able to well replicate the high quality reference data, while a buffered 14-7 potential was found to yield much better performance. It should be noted that in the calculation of van der Waals reference energies by Halgren [88], the charge penetration effects have not been separated out. It is well known that there... 

Examination and Parameterization of interatomic Potentiais for Rare Gas Dimers 133... 

Our results [77] clearly indicate that the reference vdW interaction energies for rare gas dimers can be very well modeled by the sum of a B3LYP-D3 dispersion term and a physically appealing Bom-Mayer exponential function for describing repulsive interactions. 

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