A pure H2O isolated line-shape model based on classical molecular dynamics simulations of velocity changes and semi-classical calculations of speed-dependent collisional parameters

2012 ◽  
Vol 136 (15) ◽  
pp. 154310 ◽  
Author(s):  
N. H. Ngo ◽  
H. Tran ◽  
R. R. Gamache
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Line Shape ◽  
Shape Model ◽  
Model Based ◽  
Classical Molecular Dynamics ◽  
Velocity Changes ◽  
Dynamics Simulations

scholarly journals Pressure effects on water vapour lines: beyond the Voigt profile

2012 ◽  
Vol 370 (1968) ◽  
pp. 2495-2508 ◽  
Author(s):  
N. H. Ngo ◽  
H. Tran ◽  
R. R. Gamache ◽  
J. M. Hartmann
Keyword(s):  
Water Vapour ◽  
Line Shape ◽  
Pressure Effects ◽  
Shape Model ◽  
Line Shapes ◽  
Voigt Profile ◽  
Voigt Model ◽  
Velocity Changes ◽  
Dynamics Simulations ◽  
Induced Velocity

A short overview of recent results on the effects of pressure (collisions) regarding the shape of isolated infrared lines of water vapour is presented. The first part of this study considers the basic collisional quantities, which are the pressure-broadening and -shifting coefficients, central parameters of the Lorentzian (and Voigt) profile and thus of any sophisticated line-shape model. Through comparisons of measured values with semi-classical calculations, the influences of the molecular states (both rotational and vibrational) involved and of the temperature are analysed. This shows the relatively unusual behaviour of H 2 O broadening, with evidence of a significant vibrational dependence and the fact that the broadening coefficient (in cm −1 atm −1 ) of some lines increases with temperature. In the second part of this study, line shapes beyond the Voigt model are considered, thus now taking ‘velocity effects’ into account. These include both the influence of collisionally induced velocity changes that lead to the so-called Dicke narrowing and the influence of the dependence of collisional parameters on the speed of the radiating molecule. Experimental evidence of deviations from the Voigt shape is presented and analysed. The interest of classical molecular dynamics simulations, to model velocity changes, together with semi-classical calculations of the speed-dependent collisional parameters for line-shape predictions from ‘first principles’, are discussed.

On the structure of biomedical silver-doped phosphate-based glasses from molecular dynamics simulations

2014 ◽  
Vol 16 (39) ◽  
pp. 21135-21143 ◽  
Author(s):  
Richard I. Ainsworth ◽  
Jamieson K. Christie ◽  
Nora H. de Leeuw
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
First Principles ◽  
Classical Molecular Dynamics ◽  
Dynamics Simulations

First-principles and classical molecular dynamics simulations have been carried out on undoped and silver-doped phosphate-based glasses with 50 mol% P2O5, 0–20 mol% Ag2O, and varying amounts of Na2O and CaO.

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