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We present a calculation of the structure of liquid As and Sb obtained from the electronic structure described in the tight-binding approximation. We find pair correlation functions of liquid As and Sb in excellent agreement with the experimental data. We show that the structure of liquid As still shows a Peierls distortion whereas liquid Sb is no longer distorted. In our model, the difference between As and Sb can be attributed to a harder repulsive potential of Sb which penalizes the Peierls distortion.

We study the instabilities of p-bonded systems with a particular emphasis on the structure of group-V and -VI elements. We show that the trivalency of As (respectively divalency of Se and Te) is due to the Peierls instability of a half-filled band (respectively two-third-filled band). A moment calculation shows that the periodicity is not a necessary condition for the Peierls instability. Consequently, the trivalency of As (respectively, divalency of Se, Te) also holds in disordered structures (liquid, amorphous structures), as has been shown experimentally. We also study the pressure dependence of the instability: a bifurcation point is observed for a given pressure, above which no distortion appears.

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