title: Molecular dynamics at constant Cauchy stress.
abstract: The Parrinello-Rahman algorithm for imposing a general state of stress in periodic molecular dynamics simulations is widely used in the literature and has been implemented in many readily available molecular dynamics codes. However, what is often overlooked is that this algorithm controls the second Piola-Kirchhoff stress as opposed to the true (Cauchy) stress. This can lead to misinterpretation of simulation results because (1) the true stress that is imposed during the simulation depends on the deformation of the periodic cell, (2) the true stress is potentially very different from the imposed second Piola-Kirchhoff stress, and (3) the true stress can vary significantly during the simulation even if the imposed second Piola-Kirchhoff is constant. We propose a simple modification to the algorithm that allows the true Cauchy stress to be controlled directly. We then demonstrate the efficacy of the new algorithm with the example of martensitic phase transformations under applied stress.
authors.affiliation: Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, Ontario K1S5B6, Canada.
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Miller
authors.affiliation: Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Ellad B
authors.initials: EB
authors.lastname: Tadmor
authors.affiliation: Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, Ontario K1S5B6, Canada.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Gibson
authors.affiliation: Center for Materials Physics and Technology, Naval research Laboratory, Washington, DC 20375, USA.
authors.forename: Noam
authors.initials: N
authors.lastname: Bernstein
authors.affiliation: STI IGM LAMMM, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: Pavia