  We report constant-volume and constant-pressure simulations of the
thermodynamic and dynamic properties of the low-temperature liquid and
crystalline phases of the modified Stillinger-Weber (mSW) model. We have found
an approximately linear increase of the effective Gaussian width of the
distribution of inherent structures. This effect comes from non-Gaussianity of
the landscape and is consistent with the predictions of the Gaussian
excitations model representing the thermodynamics of the configurational
manifold as an ensemble of excitations, each carrying an excitation entropy.
The mSW model provides us with both the configurational and excess entropies,
with the difference mostly attributed to vibrational anharmonicity. We
therefore can address the distinction between the excess thermodynamic
quantities often used in the Adam-Gibbs (AG) equation. We find a new break in
the slope of the constant pressure AG plot when the excess entropy is used in
the AG equation. The simulation diffusivity data are equally well fitted by
applying a new equation, derived within the Gaussian excitations model, that
emphasizes enthalpy over entropy as the thermodynamic control variable for
transport in viscous liquids.
