A simple model is presented in which the instantaneous dipole moment of the exchange hole is used to generate a dispersion interaction between nonoverlapping systems. The model is easy to implement, requiring no electron correlation (in the usual sense) or time dependence, and has been tested on various atomic and molecular pairs. The resulting C6 dispersion coefficients are remarkably accurate.
"However, since the dispersion forces are always attractive they enhance the cohesive energy of the system (liquid or solid), a densification effect which could remedy to some of the inaccuracies encountered here with the use of GGA BLYP. Several routes (empirical or semi empirical) are proposed in the literature to estimate the dispersion contribution to the interaction energy (Becke and Johnson, 2005, 2007; Grimme, 2006; Civalleri et al., 2008): they are currently under investigation. "
[Show abstract][Hide abstract] ABSTRACT: The structural and dynamical properties of four silicate liquids (silica, rhyolite, a model basalt and enstatite) are evaluated by ab initio molecular dynamics simulation using the density functional theory and are compared with classical simulations using a simple empirical force field. For a given composition, the structural parameters of the simulated melt vary little between the two calculations (ab initio versus empirical) and are in satisfactory agreement with structure data available in the literature. In contrast, ionic diffusivities and atomic vibration motions are found to be more sensitive to the details of the interactions. Furthermore, it is pointed out that the electronic polarization, as evaluated by the ab initio calculation, contributes significantly to the intensity of the infrared absorption spectra of molten silicates, a spectral feature which cannot be reproduced using nonpolarizable force field. However the vibration modes of TO4 species and some structural details are not accurately reproduced by our ab initio calculation, shortcomings which need to be improved in the future.
[Show abstract][Hide abstract] ABSTRACT: We investigated the structural and the binding properties of tetrahedral P4 molecular pairs by employing density functional theory (DFT) calculations using both the local density approximation (LDA) and the generalized gradient approximation (GGA). To consider the van der Waals interaction, we employed the GGA with dispersion correction, specifically Grimme’s approach (DFT-D2). This DFT-D2 in conjunction with the GGA (GGA-D2) well fixes the failure of the GGA in reproducing a reasonable binding energy curve. The binding energy and the equilibrium intermolecular distance are found to be in close correlation with the number of adjacent atomic pairs between two molecules. Application of the LDA and the GGA-D2 to a molecular crystal β-P4 and comparison with experiments confirms that the GGA-D2 should be used for a reliable description of P4-based molecular systems.
Journal- Korean Physical Society 02/2012; 60(3). DOI:10.3938/jkps.60.410 · 0.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This work extends our Rung 3.5 exchange-correlation density functionals by incorporating empirical internuclear “-D” dispersion corrections. The resulting PBE+
1PBE-D functionals are tested for a broad range of noncovalent interactions. The functionals provide reasonable accuracy approaching existing dispersion-corrected semilocal and hybrid functionals. Application to a molecule-surface reaction illustrates these methods’ potential.
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