IMA Postdoc Seminar (April 28, 2009)

Speaker: Abdul Rehaman Moughal Shahi (Universite de Geneve)

Title: II order Perturbation over Restricted Active Space Wavefunction : An Answer to Chemical Problems Requiring Larger Active Spaces

Abstract: Ionization potential (IP) is an essential property which helps in understanding the band structures and electronic states of molecular wires and rings. We use the newly developed RASSCF/RASPT2 method to calculate the Ionization potentials of pi-conjugated oligomeric systems of acetylene (n = 1,5) and phenylene (n = 1,3) . We check for the convergence of this method with respect to the well established CASSCF/CASPT2 method. The accuracy of this approach in calculating the IPs is comparable ~0.1 eV to that of the CASPT2. The heavy reduction in the number of configuration state functions with this approach is of great importance in studying the chemical problems, where CASSCF/CASPT2 calculations are not feasible owing to the large active spaces. In this study we have been able to study the pentamer of acetylene and trimer of Phenylene systems which can not be studied previously with the CASPT2 method