Negative heat capacity of small systems in the microcanonical ensemble

¹ Department of Biomedical Engineering and Chemistry of Life Processes Institute, Northwestern University 2145 Sheridan Road, Evanston, IL 60208, USA
² Department of Chemistry, Purdue University - 560 Oval Drive, West Lafayette, IN 47906, USA

^* cari@northwestern.edu ^** igladich@purdue.edu

Received: 8 April 2010
Accepted: 15 June 2010

Abstract

We propose a new mechanism to explain the origin of negative heat capacity in small systems. We show how a particular structure of the potential energy surface combined with a microcanonical treatment results in negative heat capacity. Moreover, this effect occurs under true equilibrium conditions. An energy landscape with a sudden and spatially large opening leads to a negative heat capacity. The magnitude of this effect is related to the extent of the opening and the number of particles in the system.