TCBG Seminar

Why is energy extensive? A quantum chemist's view.

Professor So Hirata
Department of Chemistry
University of Illinois Urbana-Champaign
Urbana, IL

Monday, April 4, 2011
11:00 am (CT)
3269 Beckman Institute


An observable thermochemical quantity is either extensive or intensive. Extensive quantities include energy, entropy, and mass and are asymptotically proportional to the volume of the system. Intensive quantities such as temperature, pressure, and chemical potential are asymptotically constant with volume. Computational methods that are meant to predict these quantities accurately must, in the very least, ensure that the predicted values satisfy these asymptotic conditions (size consistency). In this talk, I will first address the fundamental physics question as to what makes energy extensive and thus an application of thermodynamics to chemistry valid. I will do so by clarifying the asymptotes of electrostatic, exchange, and correlation interactions in metallic and nonmetallic solids. On this basis, I will introduce extensive and intensive diagram theorems that provide unambiguous and convenient sufficient conditions for computational methods to be size consistent for extensive and intensive quantities, respectively. Time permitting, I will also discuss the results of applications of quantitative and size-consistent electronic and vibrational many-body methods to polymers and molecular crystals.

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