Quantum study of the halfium particle as a reference system in MQDT analysis of H[sub 2]

ab initioR-matrix and MQDT investigation of low-lying Rydberg states of the HeH+molecular ion

“…In H 2 , the obvious choice is to take fractional charges Z 1 = Z 2 = 1/2 on each center (whence the denomination "halfium" [9]), because we must have Z 1 + Z 2 = 1 and the molecule is symmetric. This way of accounting for the partial screening by the core electron has the advantage that it provides a realistic approximation to the quadrupole field outside the ion core, which therefore is directly taken into account in the asymptotic channel functions [18]. In HeH + we must have Z 1 + Z 2 = 2, but the distribution of the total charge on the two centers is a priori arbitrary and in fact, strictly speaking, irrelevant.…”