Condensed-Matter Physics & Materials Science Seminar

Recent work aimed at the long-range goal of simulating light-induced charge transfer in large molecules, within a mean-field density-functional-based picture, will be discussed. Some of the physical interactions that must be accounted for include(1)the calculation of electronic excited states & transition rates to these states(2)determination of how excited-state energies are modified in the presence of a polarizable medium,and(3)vibrational processes in these molecules.In this talk I will discuss a simple and accurate way of estimating molecular excited-state energies by including a correction which accounts for the Coulomb interaction between the particle & hole states. On general grounds,& from applications to an experimentally fabricated light-harvesting molecule,I will show that this correction,& the correction due to a polarizable surrounding,are particularly important for charge transfer excitations. From the standpoint of efficient inclusion of vibrational effects,I will discuss a recent “order-1” method for the calculation of electron-phonon interactions in molecules & show how it can be used to accurately determine equilibrium geometries of charged or excited molecules.The same method allows one to determine harmonic crossing points along ground & excited-state potential energy curves,& to predict whether the crossing appears at an energy range that is associated with electronic or vibrational excitations. Applications of this method to carbon nanotubes, several molecules found in molecular superconductors, many small molecules, and a light-harvesting molecule will be presented. Among the more interesting results is the efficient identification of a vibrationally and electronically stable symmetry-breaking excited state in a carbon nanotube (pictured above).This work was performed in collaboration with Dr.Tunna Baruah (U. of Texas,El Paso)& Ben Powell (U. of Queesnland,AU). Calculations were performed with NRLMOL on DoD HPCMO computing platforms.