Exploring structures and energetics of large OCS clusters by correlated methods.

An extensive minima search based on accurate estimation of binding energies in (OCS)n clusters for n = 2-5 is carried out employing MP2 and CCSD(T) levels of theory. Features of the molecular electrostatic potential of the OCS monomer are utilized for building the laterally shifted and linear aggregates of OCS. Trial structures generated through cluster building algorithm are subjected to geometry optimization at MP2 level using aug-cc-pvTZ (TZ) basis set. Molecular tailoring approach (MTA)-based single-point energies at MP2/QZ and CCSD(T)/TZ levels are calculated for the estimation of binding energy at complete basis set (CBS) limit. For a comparative study, benchmark calculations employing the dispersion-corrected B2PLYPD functional with TZ basis set are effected. The resulting geometrical parameters from which are found to be in excellent agreement with the experimental findings. With increasing cluster size, the calculated vibrational frequency at the MP2/DZ level of theory shows a substantial blue shift for the asymmetric C-O stretch. The results from the present study clearly bring out the feasibility of carrying out ab initio calculations on large-sized clusters on limited hardware with a minimal loss of accuracy.