Positron-Matter Interactions

Glossary of Terms and Abbreviations for the Distributed Positron Model

DPM	Abbreviation for Distributed Positron Model. In this model, for the purpose of mimicking nonadiabatic and short-range correlation effects, the positron is treated as a non-point distribution of charge within the quantum chemistry code that calculates the polarization potential. The DPM affects only the polarization potential and is not used to describe the positron in the quantum scattering calculations.
US	Abbreviation for Uniform Spherical. This indicates a uniform, spherical distribution of charge for the positron. The radius of the distribution (in Bohr) is indicated by the value of Rp. So, for example, DPM US(Rp=1.5) or just US(1.5) indicates that in the quantum chemistry code the positron is treated as a uniform spherical charge distribution (+1) of radius 1.5 Bohr at the "fixed" location of the positron.
STO-3G	A new variant of the Uniform Spherical distribution based on a 3 Gaussian contraction of the STO for H1s. This new scheme closely approximates the US(1.5) result, but allows all of the DPM integrals to be performed analytically. For standard, sequential computers, the STO-3G variant is about one million times faster for the calculation of the modified nuclear attraction integrals.
H1s	This indicates a uniform, nonspherical distribution of charge in the DPM where the +1 charge of the positron is distributed according to the probability density of the electron in the ground state of the hydrogen atom.
BF	This indicates a nonuniform, nonspherical distribution of charge in the DPM where the +1 charge of the positron is represented by a linear combination of Gaussian basis functions. The particular linear combination at a given positron location is determined by perturbing a Positronium atom with a fractional charge that represents the "unscreened" nuclear charge of the target.
Gamera	Gamera is our new 32-node Beowulf cluster constructed from 32 1-GHz commodity-off-the-shelf machines. Gamera has 16 GB of ram and 640 GB of disk storage.
DCS	Abbreviation for Differential Cross Section.
ICS	Abbreviation for Integrated Cross Section.
Lmax	The maximum angular momentum value used in the single-center expansion of the scattering function.
Lambda max	The largest term retained in the single-center expansion of the interaction potential.
BC	Abbreviation for Born-Closure.
Rp	The radius of the uniform spherical charge distribution in Bohr.
rp or C	The location of the positron (in Bohr) with respect to the origin of coordinates.
rc	The distance (in Bohr) from the location of the positron at rp to an electron located at re.
re	The location of an electron with respect to the origin of coordinates.
COAD	Abbreviation for CutOff Adiabatic polarization potential. The cutoff function is "tuned" to experimental results.
POM	Abbreviation for Polarized Orbital Method. This method is another approximate scheme for computing a nonadiabatic polarization potential.
EMP	Abbreviation for Empirically determined model polarization potential.