17 March 1997 PHYSICS LETTERS A ELSEVIER Physics Letters A 227 ( 1997) 265-270 Density-functional theory of one-electron propagators M. Valiev, G.W. Fernando zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPO Physics Deparrmenr, University of Connecticut. Storrs, CT 06269, USA Received 3 October 1996; revised manuscript received 31 December 1996; accepted for publication 7 January 1997 Communicated by L.J. Sham zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Abstract The effective action approach to Kohn-Sham density-functional theory provides a rigorous basis for carrying out sys- tematic, first-principles calculations of the ground and excited state properties. In this work we apply the effective action formalism for developing the exact density-functional formulation of one-electron propagators. In particular, expressions for the exact Green’s function and the self-energy operator are obtained entirely in terms of Kohn-Sham derived quantities. PACS: 71.15.M 1. Introduction Over the past few decades first-principles calculations of electronic structure have generated a great deal of interest among condensed matter physicists due to the promise of predicting properties of real materials with minimal amount of experimental input. Effective action formalism [ 1] provides an entirely novel way of carrying out systematic, first-principles electronic structure work. This method should be viewed as a generalization of density-functional theory (DFT) [ 21 and offers the enticing possibility of a universal approach for calculating ground and excited state properties of many-body systems. Despite many attractive features, the practical implementation of the effective action formalism lagged behind the formal theoretical development due to a lack of understanding of the Kohn-Sham (KS) approximation scheme [3,4] within the effective action formalism [ 11. The importance of the connection to the KS single-particle picture is indisputable considering the popularity and success of KS based calculations. We would like to point out that traditionally, the KS decomposition of the energy functional is always externally imposed as a convenient way of obtaining single- particle equations: clearly, a more consistent strategy would be to have a particular way of approximating the energy functional that naturally accommodates the KS single-particle picture. Recently this problem, has been resolved and we have shown [5] that KS separation and the corresponding single-particle equations can be obtained as a result of a controlled expansion of the effective action functional. Understanding the place of the KS picture in the effective action formalism offers a new avenue for enhancing and developing the existing body of first-principles techniques. In our opinion, the possibilities are endless here. The KS version of the effective action formalism immediately leads to a controlled expansion of the exchange-correlation functional entirely in terms of KS derived quantities. We have also shown 151 that this theory is capable of a straightforward 037%9601/97/$17.00 Copyright @ 1997 Published by Elsevier Science B.V. All rights reserved. PII SO375-9601(97)00055-8