The IR spectrum of supercritical water: Combined molecular dynamics/quantum mechanics strategy and force field for cluster sampling

Patrice Bordat (1) , Didier Bégué (1) , Ross Brown (1) , Alain Marbeuf (2) , Henri Cardy (1) , Isabelle Baraille (1)

1 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux
2 LOMA - Laboratoire Ondes et Matière d'Aquitaine

Supercritical water was analyzed recently as a gas of small clusters of waters linked to each other by intermolecular hydrogen-bonds, but unexpected "linear" conformations of clusters are required to reproduce the infra-red (IR) spectra of the supercritical state. Aiming at a better understanding of clusters in supercritical water, this work presents a strategy combining classical molecular dynamics to explore the potential energy landscape of water clusters with quantum mechanical calculation of their IR spectra. For this purpose, we have developed an accurate and flexible force field of water based on the TIP5P 5-site model. Water dimers and trimers obtained with this improved force field compare well with the quantum mechanically optimized clusters. Exploration by simulated annealing of the potential energy surface of the classical force field reveals a new trimer conformation whose IR response determined from quantum calculations could play a role in the IR spectra of supercritical water.

Mots clés: water clusters; supercritical fluid; quantum chemistry; molecular dynamics

Domaines: Chimie théorique et/ou physique

Patrice Bordat, Didier Bégué, Ross Brown, Alain Marbeuf, Henri Cardy, et al.. The IR spectrum of supercritical water: Combined molecular dynamics/quantum mechanics strategy and force field for cluster sampling. International Journal of Quantum Chemistry, 2012, 112 (13), pp.2578-2584. ⟨10.1002/qua.23286⟩. ⟨hal-00713263⟩