  Random first order transition theory is used to determine the role of
attractive and repulsive interactions in the dynamics of supercooled liquids.
Self-consistent phonon theory, an approximate mean field treatment consistent
with random first order transition theory, is used to treat individual glassy
configurations, while the liquid phase is treated using common liquid state
approximations. The transition temperature $T^{*}_{A} $, the temperature where
the onset of activated behavior is predicted by mean field theory, the lower
crossover temperature $T_{c}^{*}$ where barrierless motions actually occur
through fractal or stringy motions, and $T^{*}_{K} $, the Kauzmann temperature,
are calculated in addition to $T^{*}_{g} $, the glass transition temperature
that corresponds to laboratory cooling rates. Both the isobaric and isochoric
behavior in the supercooled regime are studied, providing results for $\Delta
C_{V} $ and $\Delta C_{p} $ that can be used to calculate the fragility as a
function of density and pressure, respectively. The predicted variations in the
$\alpha$-relaxation time with temperature and density conform to the empirical
density-temperature scaling relations found by Casalini and Roland. We thereby
demonstrate the microscopic origin of their observations. Finally, the
relationship first suggested by Sastry between the spinodal temperature and the
Kauzmann temperatures, as a function of density, is examined. The present
microscopic calculations support the existence of an intersection of these two
temperatures at sufficiently low temperatures.
