First-Principles Study Of The Structural, Stability And Electronic Properties Of Small Aluminum-Titanium-Nickel Clusters

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dc.contributor.authorKoh, Pin Wai
dc.date.accessioned2022-03-21T02:15:47Z
dc.date.available2022-03-21T02:15:47Z
dc.date.issued2021-04
dc.description.abstractNanocluster has been a system of interest for the past decades due to its peculiar size-dependent properties as compared to its bulk counterparts, e.g. the chemical and electronic properties between the buckminsterfullerene C60 and graphene. However, computational, theoretical and experimental studies for pure and binary element small-size clusters are scarce, not to mention of small-size ternary element clusters. For the case of aluminium-titanium-nickel (Al-Ti-Ni) ternary element clusters, published works of small Al-Ti-Ni clusters mostly come from Erkoc and Oymak (2003; 2002, 2004) by using a fundamental empirical potential in molecular dynamic techniques, followed by performing a single point optimization at DFT level to obtain the ground-state structure for the cluster. The Al-Ti-Ni clusters generically have a very different mechanical and catalytic properties compared to their bulk counterparts, as stated in the articles by Erkoc and Oymak (2003; 2002, 2004). However, information and data about the catalytic and mechanical properties Al-Ti-Ni clusters are not shown in their articles. One of the reasons for this to have happened is that most of the ground-state structure of the binary of ternary element Al-Ti-Ni clusters that shown in their article are lack of experimental data supports. This thesis reports a systematic study of the computational modelling of small-size Al-Ti-Ni clusters at the atomistic level using a tactical two-stage computational strategy and a multitude of theoretical tools. The main focus of this thesis is to perform a systematic and thorough study on selected properties of the AlxTiyNiz clusters at the lowest energy state, where x, y and z are non-negative integers such that x + y + z = 4, 5 and 6. The ground state energy configurations of the clusters are obtained by performing a purpose-designed two-stage optimization. In the first stage, the "pg9" algorithm (a.k.a Parallel Tempering Multicanonical Basin Hopping and Genetic Algorithm (PTMBHGA) that is coupled to a density-functional theory (DFT) calculator (Gaussian 09, abbreviated G09)) to study the low-lying structures (LLS) of the cluster statistically by exchange-correlation functional -SVWN with a suitable basis-set candidate. Three different basis sets (STO-3G, 3-21G and 6-31G) with low computational complexity are employed to perform trial simulations to several cluster samples that were chosen from Al-Ti-Ni clusters system. As a result, the SVWN/3-21G is the suitable exchange functional and basis set to study the LLS statistically of the Al-Ti-Ni clusters in this thesis based on its number of basis functions and computational costs. First, the configuration of a randomly initialised cluster is globally optimized using an unbiased search algorithm BHGA (Basin Hopping and Genetic Algorithm) in "pg9" algorithm that uses an exchange-correlation functional and basis sets with low computational complexity. In the second stage, the lowest-energy configuration obtained from the first stage is further optimized using the BHGA algorithm, but a higher quality of exchange-correlation functional and basis set are employed at the second-stage simulation instead. A better quality exchange-correlation functional with two basis sets – B3LYP/LANL2DZ and B3LYP/6-311G* are employed to perform trial simulations on several cluster samples for the second-stage simulations. At last, B3LYP/6-311G* is chosen as a suitable exchange-correlation functional and basis set in second-stage simulations because this set of exchange-correlation functional and basis set able to produce the cluster with more symmetry and total energy with lower value compared to the B3LYP/LANL2DZ. The two-stage procedure can produce reliable ground state structures of small AlxTiyNiz clusters at the DFT level. After the ground state configurations of the optimized clusters are obtained, their energetic and geometrical are investigated and compared. In addition, the electronic structures of the Al-Ti-Ni clusters are also studied by performing a series of calculations for their chemical order, ionization potential, electron affinity, global hardness, etc. In the appendix of this thesis, molecular dynamics technique also performed on certain clusters of this Al-Ti-Ni clusters system by using "plmp" algorithm (a.k.a PTMBHGA integrated with Large-scale Atomic /Molecular Massively Parallel Simulator (LAMMPS) as energy calculator). Next, the total energy value of these clusters is obtained by performed an optimization on them at DFT level by using "pg9". The total energy value of these cluster structures that generated by employing a two-stage "plmp+pg9" method is higher than the same clusters that undergo the two-stage procedure at DFT level that stated in this work. In general, most of the ground state structure of pure and binary element clusters produced in this thesis are similar in term of geometry with the available literature from other researchers. The new results obtained in this thesis include (i) the ground state structure of ternary element AlxTiyNiz (𝑥+𝑦+𝑧=4,5 & 6) that are rarely or never be reported in the literature, (ii) Ni-rich clusters show minimum value in the binding energy and excessive energy, and maximum value in the second difference energy and HOMO-LUMO energy gap.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/14919
dc.language.isoenen_US
dc.publisherUniversiti Sains Malaysiaen_US
dc.subjectPhysicsen_US
dc.subjectElectronicen_US
dc.titleFirst-Principles Study Of The Structural, Stability And Electronic Properties Of Small Aluminum-Titanium-Nickel Clustersen_US
dc.typeThesisen_US
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