Banca de DEFESA: ACASSIO ROCHA SANTOS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : ACASSIO ROCHA SANTOS
DATA : 21/02/2017
HORA: 09:00
LOCAL: Auditório do química 3
TÍTULO:

STUDY OF ALUMINUM-SODIUM, ALUMINUM-POTASSIUM, ALUMINUM-LITHIUM AND SODIUM-LITHIUM

CLUSTERS BY GENETIC ALGORITHMS, QUANTUM CALCULATIONS AND TOPOLOGICAL ANALYSIS

PALAVRAS-CHAVES:

Genetic algorithm. Gupta potential. Clusters. QTAIM

PÁGINAS: 94
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Química Teórica
RESUMO:

The theoretical study of metal clusters has attracted considerable interest due to the possibility of creating new alloys from materials in nanoscale, the so-called "nanoalloys", whose theoretical research has an important role in the materials science. Some of its most relevant objectives are: to predict of stability in structures, their growth modes and to assist in the interpretation of spectroscopic and other experimental measures. A great number of methods were reported in the last few years regarding the effective global optimization of atomic and molecular systems, where  the genetic algorithm (GA) is currently one of the most used methods . The GA method, altogether with the implementation of the Gupta potential, has become efficient in the search for “optimal” solutions regarding optimization problems of metallic clusters. This GA method is based in principles related to evolutionary processes and operators inspired by the Theory of Evolution and Genetics, i. e., by recombination, mutation and natural selection. In a previous work developed for this Master’s dissertation we approached the study of AlxLiy, AlxNay and AlxKy bimetallic clusters (x + y ≤ 55) through the Genetic Algorithm method with the implementation of Gupta potential. Two operators were used in the attempt of improving the GA efficiency: history and annihilation. In another work, we performed studies with a new quantum genetic algorithm (Q-GA) for small cluster systems Na_xLi_y with (x + y ≤ 10). The Q-GA presents greater efficiency in search of the global minimum in relation to GA with the potential Gupta since the former uses quantum method while the latter uses a classical method.  The Q-GA is less comprehensive than GA because it is more precise. When comparing pure aluminum clusters from the structures obtained by the Gupta potential GA and those from recent results in the literature, we observed that the GA geometries  resembled those obtained by density functional calculations and ab initio [such CCSD(T)]. In the second work, topological calculations were performed by the Quantum Theory of Atoms in Molecules (QTAIM) for the Na₁Li₅, Na₂Li₄, Na₃Li₃, Na₄Li₂ and Na₅Li₁ structures obtained by Q-GA. We verified that there is no direct connection between the atoms rather there is an indirect bond through pseudo-atoms, exclusively defined in QTAIM. We noticed that the analysis of isodensity surface graph the of valence shell charge concentration (VSCC) is located between the lithium atoms. Then we demonstrated that unlike Li-Na bond the Li-Li bond presents a covalent character. The formation of VSCC was not observed on the isodensity surface for Na₅Li₁ system, since it has only one lithium atom in the structure. In this situation, the charge is uniformly distributed throughout the atoms of the system.

MEMBROS DA BANCA:
Presidente - 1714867 - CAIO LIMA FIRME
Interno - 1803692 - FABRICIO GAVA MENEZES
Externo à Instituição - GERD BRUNO DA ROCHA - UFPB
Externo ao Programa - 1108747 - ROBSON FERNANDES DE FARIAS