Mussa, Hamse Yussuf; (1999) Rotation-vibration states of triatomic molecules using massively parallel computers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

A formulation of the the nuclear motion (rotation-vibration) of triatomic molecules is discussed in the different implementations of the Discrete Variable Representation (DVR). The formulation is expressed in a set of internal co-ordinates using an exact nuclear motion Hamiltonian operator. We present a computer implementation of the Hamiltonian on some of the most powerful massively parallel computers in the world today. The Cray-T3E/T3D, and the IBM SP2 are used for this study. Accurate calculations of the rotation-vibrational energy levels up to the dissociation for the non-linear triatomic molecules, H2O and O3, with deep potential surfaces are presented. We also present results for two linear molecules, HN+2 and HCP. The water molecule is used as a detailed case study. Rotation-vibration studies are made using a number of realistic global potential energy surfaces. Radau co-ordinates are used for the calculations in the preconditioned DVR representation. After comprehensive variational convergence tests on the energy levels, all the J=0 bound states of the system are converged to within l cm-1 or better, giving about 1,000 states for each potential. Graphical analyses of the eigenfunctions are then made. Similar studies are performed for the J> 0. These are the first accurate rotation-vibrational calculations up to the dissociation obtained for this system. For the J> 0 case, convegence problems are found in previous, more limited, studies of the system.

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