Pressure dependence of the mean excitation energy of atomic systems

Changes in the mean ionization energy of atoms in compressed matter are estimated through cage models of atomic confinement whereby pressure is obtained in terms of the rate of change of total atomic energy with volume. Resort is taken to a recently implemented shellwise Thomas-Fermi-Dirac-Weizsacker theory for confined atoms to construct the atomic energy functional, which is self-consistently optimized for different confinement conditions. The resulting modified atomic orbital densities are then used within the Local Plasma Approximation to evaluate the corresponding orbital and total mean excitation energies. Good agreement is obtained with accurate calculations for free atoms. For compressed atoms agreement is found with a previously derived universal expression [J.M. Peek, Phys. Rev. A 36 (1987) 5429] for total mean excitation energies suggesting its adequacy for this class of studies.