Pressure effects on the electronic and structural properties of molecules

Pressure effects on the ground-state energy and molecular conformation of methane, ammonia and water are simulated through a molecular confinement model whereby an isolated molecule is caged in a hard spherical box of varying radius. A self-consistent ab initio calculation subject to Dirichlet boundary conditions is performed for each cage radius using a subminimal Floating Spherical Gaussian Orbital representation. Maximum bond compressibilities for water (β≈4×10−4 GPa−1), ammonia (β≈8×10−4 GPa−1) and methane (β≈1.3×10−3 GPa−1) are predicted at P=40, 25 and 15 GPa, respectively. The pressure-induced changes in the dipole moment of water and ammonia are also discussed.