The reference (specifically in the context of "mp4" and "solid article") most likely refers to the Gaussian 98 computational chemistry software package used for molecular modeling and quantum chemistry calculations.

: While Gaussian is primarily for gas-phase molecules, it is often cited in papers discussing the transition from gas-phase properties to the solid state , such as the bonding in rare gas halides.

In scientific literature, "Gaussian 98" is frequently abbreviated as . Researchers use it to perform various high-level calculations, including MP4 (Møller–Plesset fourth-order perturbation theory), which is a sophisticated method for describing electron correlation in molecules. Scientific Applications of G98 and MP4