Applicability of medium-size basis sets in calculations of molecular dynamic polarisabilities

Static and dynamic polarisabilities of seven linear non-polar and polar molecules are calculated within the CCS, CC2 and CC3 approximations using a range of medium-size basis sets: the polarised LPol-n (n=ds, dl, fs, fl), the aug-pc-n (n=1, 2), and the def2-SVPD and -TZVPD basis sets. Reference values are obtained using a hierarchy of Dunning's (d-)aug-cc-pVXZ (X=D, T, Q, 5) basis sets. Results are discussed together with the available CCSD results in order to recognize the most efficient approach for evaluation of molecular electric polarisabilities. The LPol-ds, LPol-dl, TZVPD and aug-pc-2 basis sets are shown to give the best compromise between the accuracy of results and the total cost of calculation for the average polarisability at all four levels of approximation, allowing for an increase of accuracy of results with respect to the aug-cc-pVTZ basis set at no cost, or even with its reduction. Accurate evaluation of polarisability anisotropy is more computationally demanding and the use of at least the aug-pc-2 basis set becomes necessary. The larger LPol-fs and LPol-fl basis sets yield even smaller values of the root mean square error calculated with respect to the largest basis set used for the given method.