He has also made contributions in the area of reactivity descriptors; he established Hirshfeld population in the calculation of Fukui functions and developed the local hard-soft-acid-base principle for molecular recognition.[6] He also studied anti-aromaticity in metal clusters.[7]
He has studied various properties of hardness and softness in relation to molecular properties, like polarizability. In 2002, he identified "Bond Deformation Kernel" to be correlated with interaction-induced shifts in O–H frequencies in halide–water clusters. His model used local polarization, which can be described by normalized-atom-condensed Fukui functions, which is the normal condensed Fukui function multiplied by the number of atoms.[11]
On molecular properties and dynamics
In 1989, he developed theories for describing closed-shell molecules with non-linear electric properties. For open-shell systems, which are marked by a high degree of quasi-degeneracy, he used a multi-determinant description of reference space to formulate a coupled-cluster analytic derivative to compute the non-linear properties.[12] Sourav has also identified the exchange effects as contributions to the static exchange potential of the molecule in electron–molecule scattering. An approximation method to calculate the resonance of molecular anions has been developed by his group. The procedure is based on the analytical continuation method.
In 2003, as an alternative to the Kohn–Sham density functional theoretic approach, which solves the coupled-perturbed Kohn–Sham (CPKS) procedure non-iteratively, Sourav formulated a way to obtain the derivative of the KS matrix using the finite field; the density matrix derivative is obtained by a single-step CPKS solution followed by the analytic evaluation of properties.[13] He has implemented this in deMon2k software and used it for the calculation of electric properties. He also has used Gaussian basis sets and Born–Oppenheimer approximation to study the reactions of molecules. His study led to novel evidence of anti-aromaticity in metal clusters.[7]
^Chandrakumar, K. R. S.; Pal, Sourav (2002). "Study of Local Hard−Soft Acid−Base Principle to Multiple-Site Interactions". The Journal of Physical Chemistry A. 106 (23): 5737–5744. Bibcode:2002JPCA..106.5737C. doi:10.1021/jp014499a.