Denise Assafrão

The isotopic dipole moment of HDO

An adiabatic variational approximation is used to study the monodeuterated water molecule, HDO, accounting for the isotopic effect. The isotopic dipole moment, pointing from D to H, is then calculated for the first time, yielding (1.5 ± 0.1) × 10−3 Debye, being helpful in the interpretation of experiments.

Adiabatic Corrections to Density Functional Theory Energies and Wave Functions

The adiabatic finite-nuclear-mass-correction (FNMC) to the electronic energies and wave functions of atoms and molecules is formulated for density-functional theory and implemented in the deMon code. The approach is tested for a series of local and gradient corrected density functionals, using MP2 results and diagonal-Born-Oppenheimer corrections from the literature for comparison. In the evaluation of absolute energy corrections of nonorganic molecules the LDA PZ81 functional works surprisingly better than the others. For organic molecules the GGA BLYP functional has the best performance. FNMC with GGA functionals, mainly BLYP, show a good performance in the evaluation of relative corrections, except for nonorganic molecules containing H atoms. The PW86 functional stands out with the best evaluation of the barrier of linearity of H2O and the isotopic dipole moment of HDO. In general, DFT functionals display an accuracy superior than the common belief and because the corrections are based on a change of the electronic kinetic energy they are here ranked in a new appropriate way. The approach is applied to obtain the adiabatic correction for full atomization of alcanes C(n)H(2n+2), n = 4-10. The barrier of 1 mHartree is approached for adiabatic corrections, justifying its insertion into DFT.

Relaxed electric dipole moments of polar molecules interacting with a slow positron: H2O and CH3X (X=F, Cl, Br)

The variation in the electric dipole moments of H2O, CH3F, CH3Cl and CH3Br as their geometries relax due to interaction with a positron is evaluated. The results are in good agreement with a recently observed empirical dependence of the positron binding energy on molecular properties (Danielson et al 2009 J. Phys. B: At. Mol. Opt. Phys. 42 235203). For binding energies larger than 100 meV relaxation could alter significantly the analysis of the binding, but it is in the prospect of generating effective potentials for positron scattering by molecules that the effect can be more important.

Semiempirical potentials for positron scattering by atoms

We report calculations of differential and integral cross sections for positron scattering by noble gas and alkaline-earth atoms within the same methodology. The scattering potentials are constructed by scaling adiabatic potentials so that their minima coincide with the covalent radii of the target atoms. Elastic differential and integral cross sections are calculated for Ne, Ar, Be, and Mg, and the results are very close to experimental and best theoretical data. Particularly, elastic differential cross sections for Be and Mg at low energies are reported.

Coincidence studies with antiprotons

We present a short overview of a new method for calculating fully differential cross sections that is able to describe any aspect of coincidence measurements involving heavy projectiles. The method is based upon impact parameter close coupling with pseudostates. Examples from antiproton impact ionization are shown.

Relaxed geometries and dipole moments of positron complexes with diatomic molecules

Relaxed geometries and dipole moments of diatomic molecules interacting with a slow positron are reported as functions of the positron distance to the more electronegative atom. A molecular model for the complex that allows applications to large systems is used. The electron population on the positron is proposed as a weighting function to calculate the average quantities. Results show Self-Consistent-Field quality or better.

Antiproton impact ionization of atomic hydrogen and helium

We shall present results for antiproton ionization of H and He ranging from fully differential cross sections to total ionization. The calculations have been made in a coupled pseudostate impact parameter approximation. It will be shown that the interaction between the antiproton and the target nucleus is very important at low energies.

Ionization of helium by Au24+ and Au53+ projectiles

A coupled pseudostate impact parameter approximation has been used to calculate triple differential cross sections for single ionization of He by Au24+ and Au53+ projectiles.