The influence of both coordination number and lattice constant on the nonmetal to metal transition

We show that both coordination and lattice constant can have an important i nfluence on the nonmetal to metal transition and the two parameters are not easily separated. Using example theoretical calculations for barium, we pr ovide a compelling case that atomic coordination is a critical factor in de termining the critical lattice constant for the nonmetal to metal transitio n. A comparison between the nonmetal to metal transition three-dimensional and two-dimensional systems is not possible on the basis of the atomic coor dination alone. This is discussed in the context of a comparison of the ava ilable experimental data for both elemental expanded fluids (three-dimensio nal) and overlayers (quasi-two-dimensional). (C) 2000 American Institute of Physics. [S0021-9606(00)71217-7].