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Multidimensional generalized-ensemble algorithms for complex systemsMitsutake, Ayori, Okamoto, Yuko 04 June 2009 (has links)
No description available.
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Spectroscopic and ab initio studies on the conformations and vibrational spectra of selected cyclic and bicyclic moleculesAl-Saadi, Abdulaziz A. H. 15 May 2009 (has links)
The structure, potential energy functions and vibrational spectra of several cyclic
and bicyclic molecules have been investigated using several spectroscopic techniques
and high-level ab initio and density functional theory (DFT) calculations. Laser induced
fluorescence and Raman spectroscopies were used to study the conformation of 2-
indanol in the electronic ground and excited states. These, along with detailed ab initio
calculations, confirmed the existence of four different stable conformations with the one
undergoing an intermolecular hydrogen bonding being the most stable. A theoretical
two-dimensional surface in terms of the ring-puckering and the hydroxyl group internal
rotation vibrations was constructed. This work was extended to obtain preliminary
insights on the conformations and ring-puckering frequencies of 3-cyclopenten-1-ol
using ab initio and DFT calculations.
Infrared and Raman spectra were also utilized to study the structures and
vibrational spectra of -crotonolactone and 2,3-cyclopentenopyridine (pyrindan). Ab initio results showed that -crotonolactone is rigidly planar in the electronic ground state
and has a nearly harmonic ring-puckering potential function. The calculated vibrational
levels were shown to be in very good agreement with the experimental ring-puckering
frequency from vapor-phase Raman observations.
The structures, vibrational spectra, and potential energy functions of several
cyclic molecules were reinvestigated using high-level ab initio computations, and
detailed vibrational analyses based on DFT-B3LYP calculated frequencies were also
carried out. A number of new insights were presented by re-evaluating the available
experimental data for several cyclopentenes, silacyclobutanes and silacyclopentenes. It
was found that the vibrational spectra of some deuterated cyclopentenes possess
extensive coupling between several ring modes and other low-frequency modes.
Reassignments of these spectra have been proposed. Frequencies from DFT-B3LYP
calculations showed very good agreement with the experimental values for
silacyclobutane and its derivatives. The presence of silicon and halogen atoms did not
affect the accuracy of the DFT calculations. In addition, the ring-puckering potential
energy function for silacyclopent-2-ene was studied and alternative assignments of the
far-infrared results were proposed. The new assignments are in good agreement with
computational results. Silacyclopent-2-ene and its -1,1-d2 isotopomer were shown to be
slightly puckered with barriers of less than 50 cm-1.
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Determining Analytical Potential Energy Functions of Diatomic Molecules by Direct FittingHuang, Yiye January 2001 (has links)
The fully quantum mechanical 'direct-potential-fit' (DPF) method has become increasingly widely used in the reduction of diatomic spectra. The central problem of this method is the representation of the potential energy and Born-Oppenheimer breakdown (BOB) correction functions. There are a number of problems associated with the existing method and potential forms. This thesis delineates these problems and finds solutions to some of them. In particular, it is shown that use of a different expansion variable and a new treatment of some of the expansions resolves most of the problems. These techniques have been successfully tested on the ground electronic states of the coinage metal hydrides and the Rb2 molecule. To address the problem of representing 'barrier' potential curves, a flexible new functional form, the 'double-exponential long-range' (DELR) potential function, is introduced and applied to the B barrier state of Li2. In addition, the Lambda-doubling level splitting which occurs for singlet Pi electronic states has been taken into account by extending the effective Schrodinger equation. The computer program DSPotFit developed in our laboratory for performing DPF analyses has been extended to incorporate the ability to fit the analytical potential energy functions to tunneling predissociation line widths for quasibound levels. Finally, an attempt is made to investigate whether there exists a hump in the ground state rotationless potential curve of beryllium hydride.
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Determining Analytical Potential Energy Functions of Diatomic Molecules by Direct FittingHuang, Yiye January 2001 (has links)
The fully quantum mechanical 'direct-potential-fit' (DPF) method has become increasingly widely used in the reduction of diatomic spectra. The central problem of this method is the representation of the potential energy and Born-Oppenheimer breakdown (BOB) correction functions. There are a number of problems associated with the existing method and potential forms. This thesis delineates these problems and finds solutions to some of them. In particular, it is shown that use of a different expansion variable and a new treatment of some of the expansions resolves most of the problems. These techniques have been successfully tested on the ground electronic states of the coinage metal hydrides and the Rb2 molecule. To address the problem of representing 'barrier' potential curves, a flexible new functional form, the 'double-exponential long-range' (DELR) potential function, is introduced and applied to the B barrier state of Li2. In addition, the Lambda-doubling level splitting which occurs for singlet Pi electronic states has been taken into account by extending the effective Schrodinger equation. The computer program DSPotFit developed in our laboratory for performing DPF analyses has been extended to incorporate the ability to fit the analytical potential energy functions to tunneling predissociation line widths for quasibound levels. Finally, an attempt is made to investigate whether there exists a hump in the ground state rotationless potential curve of beryllium hydride.
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Theoretical Investigation Of Altini Ternary Clusters: Density Functional Theory Calculations And Molecular Dynamics SimulationsOymak, Huseyin 01 July 2004 (has links) (PDF)
This doctoral study consists of three parts. In the first part, structural and electronic properties of Al_kTi_lNi_m (k+l+m=2,3) microclusters have been investigated by performing density functional theory (DFT) calculations within the B3LYP [which comprises the Becke-88 exchange functional and the correlation functional of Lee, Yang, and Parr] and the effective core potential (ECP) level. Dimers and trimers of the elements aluminum, titanium, and nickel, and their binary and ternary combinations have been studied in their ground states. The optimum geometries, possible dissociation channels, vibrational properties, and electronic structure of the clusters under study have been obtained.
In the second part, after an empirical potential energy function (PEF) has been parametrized for the AlTiNi ternary system, stable (minimum-energy) structures of Al_kTi_lNi_m (k+l+m=4) microclusters have been determined by molecular dynamics (MD) simulations. The energetics of the microclusters in 1K and 300 K have been discussed. By performing, again, DFT calculations (within the B3LYP and ECP level), the possible dissociation channels and electronic properties of the obtained clusters have been calculated.
In the last part, using the empirical PEF parametrized previously for the AlTiNi ternary system, minimum-energy structures of Al_nTi_nNi_n (n= 1-16) ternary alloy nanoparticles have been determined by performing MD simulations. The structural and energetic features of the obtained nanoparticles have been investigated.
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