International Journal of Computer Applications (0975 – 8887) Volume 4– No.8, August 2010 35 Orbital Structure Analysis in Molecular Electronics Manas Ranjan Pradhan E.G.Rajan IBS, Hyderabad MGNIRSA, Hyderabad Survey No.156/157, Dontanaplli, ShankarPalli Gagan Mahal road, Domalguda ABSTRACT The objective of this research work is to find out the orbital structure effect of the molecules used in a molecular wire of polyphenylene chain which facilitate the electron flow in a molecular surface and in turn gives electronic properties. Taking molecular rectifier diode as the part of study, we have analyzed the hybridization property maintained among molecules where electrons get flowed from donor part to acceptor part with insulator as intermediate. The whole of the study takes place as donor part molecular orbital, acceptor part molecular orbital and the insulator part molecular orbital and how does it affect to the whole single molecule as Donor-Insulator-Acceptor. The use of Density function theory and Non equilibrium green’s function are mentioned to study the voltage ~ current characteristics and detailed quantitative model will be put in our next research work. Key words: Molecular Electronics, Molecular Orbital, Atomic Orbital 1. INTRODUCTION The general principle of analyzing the electron liberation in a surface is analyzed by photoelectric effect. This liberation of electrons from matter (here it is molecular wire as a whole) happens under the influence of sufficiently high frequency electromagnetic raditation, particularly ultraviolet and X-rays. Assuming the molecular surface is photosensitive; the theory of electron conductivity signifies the existence of free electrons within the metals. From the viewpoint of photoelectric itself, the liberation of electrons by the electric field of light wave is easily understood [Fig.1]. The building blocks of molecular electronics are single or small pakets of molecules [1]. A number of molecular electronics based digital circuits have already been reported in different research work worldwide. If we restrict our studies only to molecular diodes there are two types of molecular diodes: rectifying diodes and resonant tunneling diodes which can both be used in realizing monomolecular digital logic circuits [2]. The whole molecules involved in designing the molecular diode has taken as monomolecular and the properties can only study with a combination of different molecular orbital structure. The study confined here is designing molecular surface with polyphenylene-based chains. The polyphenylene chains are nothing but the chain of interlinking benzene molecules. This chain of benzene along with subsidiary donor group, acceptor group and insulator group analyzed the electronics and electrical properties of molecular surface. Here we have considered a single molecular surface consisting of donor, acceptor and insulator. The electron flows happens from donor side to acceptor side with insulator intermediate. The electrical or electronic properties get analyzed only if we analyze the orbital features of all the molecular orbital involves. The molecular orbital features and its wave properties generally get studied by quantum mechanics and helps in analyzing the energy at different states starting from ground state of molecular combination to most excited state. With different voltage applied with internal resistor as insulator group molecule and external register, we will able to analyze variation of current with intensity of light (X-rays) and variation of current with negative potential at collector side. We can also analyze the stopping potential for kinetic energy study of most energetic electron and how does it affect molecular energy.