Derivation of selenium–selenium nonbonded potential parameters for molecular crystals

Abstract

Potential-function parameters for Se-Se non-bonded atom-atom pair interactions have been derived from the room-temperature heat of sublimation of a mixture of monoclinic a-and fl-Se s and from the crystal structures of these two modifications. The first procedure applied was that of Nauchitel ' & Mirskaya [Soy. Phys. Crystallogr. (1972), 16, 891-892]; the second was that of Williams [J. Chem. Phys. (1967), 47, 4680-4684]. In the latter procedure, the exponential parameter for the Se-Se repulsive term from the previous procedure was used and the coefficients of the attractive and repulsive terms were fitted to 22 observational equations by a weighted least-squares calculation. The second procedure proved to be more reliable than the first. Unlike the first procedure it yielded parameters with which a heat of sublimation of a-Se a could be calculated that was 0-8 kcal mol -~ higher than that of fl-Se a. At the same time, the calculated heats of sublimation of both modifications deviate by less than 2% from the experimental value of the monoclinic mixture. A low average value of 2.7% for the standard deviation of the parameters derived was obtained.

Lattice-energy calculations on phenothiazine and phenoselenazine modifications

“…Coefficients fitted by Williams (1972a) for the C and H atoms and by Govers (1975) for the N atom were selected. For the S...S interactions potential parameters were taken from Rinaldi & Pawley (1973), and for the Se...Se interactions parameters proposed by Govers (1979) were used. For mixed interactions the geometric-mean combining law was used for coefficients A and C, while B was fitted to give the minimum of the potential function at the sum of the respective van der Waals radii.…”

Gitterenergieberechnungen zur Ermittlung der wahrscheinlichsten Strukturtypen für Verbindungen MX 6

“…Es kommt uns nicht auf Absolutberechnungen an; wir wollen nur verschiedene, im Prinzip ~ihnliche Strukturtypen mit immer den gleichen Molek/jlen MX 6 vergleichen; dies ist mit irgendeinem Satz von Parametern aus der Literatur mSglich. F/jr Schweratome sind aus der Literatur kaum Parameter bekannt; zu den wenigen bekannten Werten gehSren diejenigen f/Jr Selen (Govers, 1979). Wir haben bei allen unseren Berechnungen f/Jr die M-Atome die Parameter f/Jr Selen und f/Jr die X-Atome die Parameter f~r Chlor nach Bates & Busing (1974) (Kitaigorodsky, 1973;Williams & Houpt, 1986).…”