Bond repulsion, electron correlation, and dimerization in low-dimensional solids under pressure

It is pointed out that a test of some current ideas concerning dimerization in low-dimensional solids may be accessible via pressure experiments. To demonstrate this, the bond-charge repulsion, together with on-site and nearest-neighbor site repulsion, have been calculated as a function of interatomic separation for examples with parametrization appropriate to iodine and hydrogen. There is a crossover in behavior in each case corresponding to Coulomb repulsion either favoring or opposing dimerization, though the quantitative details are very different for the two materials. The results are discussed in relation to earlier work on the insulator-metal transition induced by pressure.