Theoretical Study On The Binary Cluster And Hydrogen Bonded Radical Complexes

In this paper, binary clusters and hydrogen bonded radical complexes have been studied using high-level ab initio methods and density functional theory (DFT). The important and valuable results have been summarized as follow:1. Electronic structure and stability of Al_nX_n (X=P, As; n=1-4) clustersThe structures and energies of mixed group â…¢ - â…¤ clusters using density functional theory (DFT) have been studied in this paper. In particular, we have studied the monomer, dimmers, trimers and tetramers of A1P and AlAs. The geometric structures, electronic configurations, harmonic vibrational frequencies, chemical bonding and cluster stabilities are presented. The similarities and differences between mixed group â…¢ - â…¤ clusters and those of carbon or silicon clusters are also important aspects which need to be investigated. Comparison is made with the results for mixed group â…¢ - â…¤ clusters and those of carbon or silicon clusters clusters. The results can be summarized as follow:(1) Al_nP_n (n=1-4) clustersThe geometry, electronic configurations, harmonic vibrational frequencies and stability of the structural isomers of aluminum phosphide clusters have been investigated using density functional theory. For dimers and trimers, the lowest energy structures are cyclic (â…¡ s,â…¦s) with D_nh symmetry. The caged structure with Td symmetry (Xs) lie lowest in energy among the tetramers. The Al-P bond dominates the structures for many isomers so that one preferred dissociation channel is loss of the A1P monomer. The hybridization and chemical bonding in the different structures are also discussed. Comparisons with silicon and boron nitride clusters, the ground state structures of Al_nP_n clusters are analogous to those of their corresponding Si_2n counterparts. This similarity follows the isoelectronic principle.(2) AlnAsn(n=l-4) clustersThe geometry, electronic configurations, harmonic vibrational frequencies and stability of the structural isomers of AlnAsn clusters (n=l-4) have been investigated using density functional theory. For dimers and trimers, the lowest energy structures are planar cumulenic rings (II s, Vis ) with Dnh symmetry. The caged structure with Td symmetry (IXs) lie lowest in energy among the tetramers. The Al-As bond dominates the structures for many isomers so that one preferred dissociation channel is loss of the AlAs monomer. The atomic charges, hybridization and chemical bonding in the different structures are also discussed. The similarities and differences between mixed group III- V clusters have been compared. It is found that the properties of the aluminum arsenide clusters are analogous to those of their corresponding AlnPn counterparts.2. A13B and AlnNn (n=3-9) clusters(1) Structures and stabilities of AI3B isomersA theoretical study of the AI3B system has been carried out by means of density functional (B3LYP) and ab initio methods (MP2) in combination with relatively large basis sets. The structures of several singlet and triplet species are reported, together with their vibrational frequencies and relative energies. There are two species lying quite close in energy: a pyramidal isomer, 4t ( 3Aj), a trigonal isomer, Is ( lA\), in which boron is found to be three-fold coordinated and aluminum behave as a monovalent atom. The pyramidal triplet specie is predicted to be the best candidate for the global minimum at all levels.( 2 ) Structure and vibrations of AlnNn (n=3-9) clustersThe structure and harmonic vibrations of AlnNn (n=3-9) clusters have been investigated using the B3LYP (Becke 3-parameter-Lee-Yang-Parr) density functional theory. All structures are found to be cumulenic Dnh rings (equal bonds, alternating angles), with one intense out of plane mode and three infrared-active degeneratemodes, of which the highest one is extremely intense and asymptotically increases to 1217 era'1 for n=9. Comparisons with C2n clusters and BnNnclusters, the structure and bonding type for the AlnNn clusters are consistent with those of the C2n (n=3,5,7,--) clusters and the BnNnclusters.3. Existence of HO2"X ( X=H2O2, HF, H2CO3) radical complex(1) HO2*H2O2 radical complexThe structure, vibrational spectrum and binding energy of HOi'FbC^ radical complexes are predicted for the first time using ab initio molecular orbital methods. Two equilibrium structures of the HC^'^Ch radical complexes have been determined, structure 1 is a six-membered ring with two distorted hydrogen bonds, structure 2 is a five-membered ring with the other atoms in the H2O2 out of the plane. Theory predicts that the binding energy Do of structure 1 and 2 is 5.3 and 4.67 kcal/mol respectively using CCSD(T) method(2) HO2*HF radical complexThe structure, vibrational spectrum and binding energy of two energetically low-lying minima (structure 1 and 2) are calculated for the first time using UB3LYP and UMP2(FULL) methods. The basis sets used are 6-311++G(d,p), 6-311++G(2d,2p). At all levels of theory, structure 1 (2A") is located as global minimum, with a binding energy De of about 8.1 kcal/mol. With zero point energy correction, the bonding energy is 5.3 kcal/mol using CCSD(T)//B3LYP method. Structure 2 (2A ) is predicted to lie about 1.2 kcal/mol higher in energy, with a hydrogen bonding occurring between the hydrogen atom in the hydrogen fluoride molecule and the terminal oxygen atom in the hydroperoxy radical. The HF stretching frequencies of the HF molecule for structure 1 and 2 are red-shifted by 466 and 322 cm"1 respectively from the isolated molecule. Its infrared intensity is enhanced by 5.4 and 7.3 times that of the monomer respectively.(3) HO2?H2CO3 radical complexWe present our results of the study for the first time on hydrogen bonded H2CO3-HO2 complexes (structure 1-7) by means of ab initio molecular orbital theory. These complexes are important intermediate in the reaction of hydroperoxy radical and cabonic acid. These structures that we calculated are six-membered ring (structure 1-2), seven-membered ring (structure3-4) and a hydrogen bonding structure (structure5-7). We have found that the binding energy of these seven complexes are 4.4,7.5,8.6,14.3,7.6,5.4 and 5.1 kcal/mol, respectively, using G3(MP2)//B3LYP method. We have also calculated vibrational and rotational frequencies for these complexes.The new results in the thesis have been summarized as follow:1. The relationships between the structures of group III-V clusters and their stabilities are confirmed using high level methods in this work. In particular, we have studied the monomer, dimers, trimers and tetramers of group III-V clusters. Studies on group III- V clusters is helpful to understand the mechanism of the progressive formation of aggregates and the emergence of condensed-phase properties. It can also be used to help experimentists designing the material.2. We have found for the first time that the properties of the aluminum arsenide clusters are analogous to those of their corresponding AlnPn, Si2n counterparts. The results can explain the modification and refinement of Si phase in Al-Si alloy in the molecular level. The relationships between the micro-structure and geometry parameters of clusters is established. This methods can not only act as a new way to find modifying agent and refining agent but also shorten the working time and reduce cost of experimental material.3. In this paper, 11 hydrogen bonded radical complexes have been studied using high-level ab initio methods to predict vibrational and rotational spectrum which are extremely useful for identifying trace components in many regimes and to provide theexperimentally more interesting parameters that could facilitate the experimental characterization of the complex.