  The structural and electronic properties of the carbonyl sulfide dimer anion
are calculated using density functional theory within a pseudopotential method.
Three geometries are optimized and investigated: C2v and C2 symmetric, as well
as one asymmetric structure. A distribution of an excess charge in three
isomers are studied by the Hirshfeld method. In an asymmetric (OCS)2^- isomer
the charge is not equally divided between the two moieties, but it is
distributed as OCS^{-0.6} OCS^{-0.4}. Low-lying excitation levels of three
isomers are compared using the time-dependent density functional theory in the
Casida approach.
