Accurate double many-body expansion potential energy surface of HS₂(A²A') by scaling the external correlation

A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS₂ by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pV QZ basis set. By using the double many-body expansion-scaled external correlation method, such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal· mol^-1. The topographical features of the HS₂(A²A') global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS₂(A²A') can be used as a building block for constructing the global potential energy surfaces of larger m S/H molecular systems and recommended for dynamic studies on the title molecular system.