Theoretical investigation of structures andspectroscopy of molecules and clusters : a combination of electronic structure theory and multicanonical Monte Carlo simulation

Bandyopadhyay Pradipta; バンディオパッダイ, ブラディプタ; BANDYOPADHYAY, Pradipta

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Theoretical investigation of structures andspectroscopy of molecules and clusters : a combination of electronic structure theory and multicanonical Monte Carlo simulation

https://ir.soken.ac.jp/records/192

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要旨・審査要旨 / Abstract, Screening Result (385.0 kB)
本文 / Thesis (8.1 MB)

Item type

学位論文 / Thesis or Dissertation(1)

公開日

2010-02-22

タイトル

Theoretical investigation of structures andspectroscopy of molecules and clusters : a combination of electronic structure theory and multicanonical Monte Carlo simulation

タイトル

Theoretical investigation of structures andspectroscopy of molecules and clusters : a combination of electronic structure theory and multicanonical Monte Carlo simulation

言語

eng

資源タイプ

資源タイプ識別子

http://purl.org/coar/resource_type/c_46ec

資源タイプ

thesis

著者名

Bandyopadhyay Pradipta

フリガナ

バンディオパッダイ, ブラディプタ

著者

BANDYOPADHYAY, Pradipta

学位授与機関

学位授与機関名

総合研究大学院大学

学位名

博士（理学）

学位記番号

内容記述タイプ

Other

内容記述

総研大甲第376号

研究科

値

数物科学研究科

専攻

値

07 構造分子科学専攻

学位授与年月日

1999-03-24

学位授与年度

値

1998

要旨

内容記述タイプ

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内容記述

It was known from the early days of quantum mechanics that all the information of the interactions within a molecular system were hidden in the Schrodinger equation. Only difficulty was that the equation was too complicated to solve for real molecular systems. However, development of several approximate methods coupled with the progresses in computer technology and computational algorithm has broken the myth of insolubility of Schrodinger equation for molecular systems. Nowadays computational chemistry has reached a stage where quantum chemical calculations are making great impacts not only on the forefront of chemistry but also in other fields such as material science and biological science.
Statistical mechanical simulation techniques such as Monte Carlo (MC) and Molecular Dynamics (MD) are another class of ways to investigate complex molecular systems by including the effects of external parameters such as temperature and pressure. The MC simulation gives average values of some properties, whereas MD simulation gives time dependent information. Indeed electronic structure calculations and statistical mechanical simulations are two complementary tools for studying molecular systems. The dependence of the molecular systems on the surrounding environment and external parameters can be studied accurately by the efficient combination of these two tools. As a matter of fact, the ab initio simulation techniques are in widespread use for studying various kinds of molecular systems in gas, liquid and solid phases. However, the enormous computational cost is a bottleneck for using ab initio simulations. The need for the techniques, which can reduce the computational cost by increasing the efficiency of the simulation, can hardly be overemphasized.
In the first part of the present thesis, the multicanonical MC simulation has been combined with the electronic structure calculations to develop a highly efficient ab initio simulation technique. The multicanonical MC simulation, which was introduced in the context of first order phase transition, is superior than the standard MC simulation in the sense that the former can explore any potential energy surface efficiently, however complex it may be. Also the canonical average of any property can be calculated at various temperatures from a single run using the histogram reweighting technique. Their multicanonical ab initio simulation technique is capable of exploring all parts of the potential energy surface of any complex molecular system and use of the reweighting histogram technique should give a major boost to the accurate study of the temperature dependent phenomena of them. In the second part of the thesis, potential energy surfaces of HNO molecule was investigated by the multireference configuration interaction calculation.
In the first part of his work, he has investigated isolated clusters in molecular beam condition using the combination of multicanonical MC and electronic structure methods. In the molecular beam experiments there exists an ensemble of the clusters with a distribution of energies. This ensemble is not exactly canonical nor is it microcanonical, but as a first approximation it can be treated as canonical. Some recent experimental photoelectron and infra-red spectra of isolated clusters suggest that the contributions from the entropy dominated structures need to be taken into account for explaining these spectra. Keeping the above experimental facts in mind, in the first application, they have investigated how the average structure of water dimer, which is a prototypical weakly bound complex, changes with temperature. Multicanonical MC, with RHF/6-31G* calculation at each step of the simulation, was performed for this investigation. Probability distributions of various geometrical parameters as a function of temperature were analyzed to find the structural change. It has been found from the result of the simulation that the probability of finding the structures similar to the transition state ones increases as temperature increases. This work demonstrates how the entropy dominated states corntribute to the average structure of water dirmer as a function of temperature. In the second application, they have taken the daunting task of explaining the highly complex photoelectron spectra of Si2C2-. The spectra shows four peaks, presumably from the contribution of different isomers in the experimental condition. Different structures of Si2C2- were examined to find the optimized structures at the MP2/6-31+G* level. Then multireference configuration interaction calculations with AVDZ basis set confirm that the peaks did arise from the two type of structures, namely linear and ring. In the next step, multicanonical MC simulation, with configuration interaction calculation at each step of the simulation, was performed to find the finite temperature effect on the spectra. Indeed it was found that the simulation can explain the origin of the peaks, which indicates the power of this technique in elucidating complex experimental findings.
In the second part of my work, potential energy surfaces of several low lying states of HNO were calculated by the multireference configuration interaction (MRCI) method. They have characterized the state 21A/ in this work, which should motivate the experimentalists to probe this previously unexplored state. Three parts of the potential energy surfaces were emphasized in the calculation. The potential curve along the NH stretch was investigated to understand the H+NO dissociation limit for two states of each of the symmetries 1A/, 1A//, 3A/, 3A//. The potential energy curves with respect to the variation of HNO angle were also examined to investigate the Renner-Teller effect. The position of the minimum, saddle point, and barrier height of the 2 1 A/ state were estimated after fitting the calculated points by power series expansion.
In this thesis, multicanonical/histogram reweighting technique and electronic structure calculation are combined to develop a highly efficient simulation technique. This technique can expand the power of ab initio based simulations. Especially this technique should be very useful for studying temperature dependent phenomena accurately for molecular systems. This has been demonstrated in this thesis by applying this technique at first to water dimer and then to explain the photoelectron spectra of Si2C2-. In another work state of the art ab initio calculation was performed to investigate several low lying states of HNO molecule, in particular, for the optically allowed 2 1 A/ state.

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http://purl.org/coar/version/c_ab4af688f83e57aa

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Theoretical investigation of structures andspectroscopy of molecules and clusters : a combination of electronic structure theory and multicanonical Monte Carlo simulation

× Bandyopadhyay Pradipta

× バンディオパッダイ, ブラディプタ

× BANDYOPADHYAY, Pradipta

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