Computing Large Molecules: Broken Bottlenecks

Abstract: Quantum mechanical methods are invaluable for understanding the electronic energies and properties of chemically and biologically interesting molecules. Quantum chemical calculations on atoms and small molecules employing simple methods began in 1930’s and continued till 80’s. With the advents in computing hardware and software, medium-sized molecules became amenable to computation by refined theoretical methods by the turn of the century. The cost of such high-level calculations, however, increases sharply with the system size, restricting their applicability to small- or medium-sized systems. For this purpose, cost-effective approximations, such as fragmentation-based approaches have been developed.

The talk will narrate the story of the quantum chemical calculations from 1970’s to 2015 with emphasis on a fragmentation based method (viz. molecular tailoring approach) developed in my laboratory during the last two decades. An electrostatic potential-based algorithm for systematically building energetically favorable structures of a variety of molecular clusters, followed by MTA-based geometry optimization will be presented. A grafting methodology for the accurate yet inexpensive estimation will be illustrated through vibrational IR and Raman spectra of molecular clusters and real proteins.

About the Speaker: Prof. Shridhar Gadre is currently an Emeritus Fellow, Department of Chemistry, Indian Institute of Technology, Kanpur. His research interests are in the area of theoretical and computational quantum chemistry. Prof. Gadre obtained his Ph. D. in Chemistry at I.I.T. Kanpur, under the guidance of Prof. P. T. Narasimhan, 1979. He later carried out postdoctoral research with Prof. Robert G. Parr, University of North Carolina, Chapel Hill, U.S.A. (1978-79) and Prof. Robert L. Matcha, University Houston, Houston, TX, U. S. A. (1979-80). Prof. Gadre joined University of Pune as a lecturer in 1980 and was subsequently elevated to the post of professor. As the Department Head, he catalyzed attaining the status of the UGC Centre of Advanced Study for the Department of Chemistry, University of Pune. In 2010, he joined the Department of Chemistry at IIT Kanpur. Prof. Gadre has published over two hundred research papers and authored several book chapters. He has received several prestigious fellowships and awards to his credit, including J. C. Bose National Fellowship by the DST, New Delhi (2007), Shanti Swarup Bhatnagar Prize in Chemical Sciences (1993) and Young Scientist Award in Chemical Science, of the Indian National Science Academy, New Delhi, (1982).

Professor Gadre’s research contributions center around the molecular electron density distributions in position and momentum spaces. He has explored topographical characteristics of molecular electrostatic potentials and developed connections with several important chemical concepts such as anionic shapes, sizes and reactivity, Hammett constants, Clar’s sextet theory, aromaticity, reaction mechanisms and molecular recognition. His group pioneered the indigenous development of parallel ab initio codes, including a Hartree-Fock code on the parallel computer PARAM that became available at CDAC, Pune in 1991. Since 1994, his team has been engaged in the development of efficient algorithms and parallel programs, christened by them as molecular taioloring approach (MTA). This code enables ab initio level geometry optimization and vibrational frequency calculation on large molecules and molecular clusters, which is not possible by employing standard ‘black-box codes.