Biomedical subjects

K Szalewicz

Publications and source records attributed to K Szalewicz.

At least 19 recordsLinked to original sources

PubMed2001

Breit-Pauli and direct perturbation theory calculations of relativistic helium polarizability.

Large Gaussian-type geminal wave function expansions and direct perturbation theory (DPT) of relativistic effects have been applied to calculate the relativistic contribution to the static dipole polarizability of the helium atom. It has been demonstrated that DPT is superior for this purpose to traditional Breit-Pauli calculations. The resulting value of the molar polarizability of 4He is 0.517254(1) cm3 x mol(-1), including a literature estimate of QED effects. As a by-product, a very accurate value of the nonrelativistic helium second hyperpolarizability, gamma = 43.104227(1) atomic units (without the mass-polarization correction), has been obtained.

Journal Article↗

PubMed2001

Intermolecular potentials with flexible monomers.

Most available intermolecular potentials assume rigid monomers. Such an assumption is a reflection of a trivial observation that if monomer degrees of freedom are considered, the dimensionality of an intermolecular potential increases dramatically even for few-atom monomers. This puts strict limits on the sizes of clusters with flexible monomers that can be treated by ab initio methods since the number of grid points needed to fit a potential surface quickly becomes enormous. Most of the literature flexible-monomer potentials were obtained from the so-called site-site rigid-monomer potentials by simply allowing the sites to move with atomic nuclei as the monomers are deformed. This simple atom-following approach has been investigated in the present work, using water dimer and Ar-HF as test systems, and shown to be not adequate. A method has been proposed which uses properties of isolated flexible monomers to improve upon the atom-following approach without performing any dimer calculations outside the rigid-monomer grid. The method is shown to give for Ar-HF a 3D representation of the dispersion energy that should be adequate for HF motion in the ground and first excited vibrational states.

Journal Article↗

PubMed2000

Water pair and three-body potential of spectroscopic quality from Ab initio calculations

We present the first pair plus three-body potential of water from ab initio calculations that quantitatively reproduces the experimental far-infrared spectra of the water dimer and trimer. The dimer spectrum was obtained from the pair potential through rigorous six-dimensional quantum calculations of the vibration-rotation-tunneling levels. The three-body interactions, together with the pair potential, produce an accurate representation of the hydrogen bond torsional levels of the water trimer.

Journal Article↗

PubMed2000

Density shift and broadening of transition lines in antiprotonic helium

The density shift and broadening of the transition lines of antiprotonic helium have been evaluated in the impact approximation using an interatomic potential calculated ab initio with the symmetry-adapted perturbation theory. The results help to remove an uncertainty of up to 10 ppm in the laser spectroscopy data on antiprotonic helium and are of importance in experimental tests of bound state QED and CPT invariance.

Journal Article↗

PubMed1993