Density Functional Study Of The Fullerene Derivatives Nanomaterials

With the progress in density functional theory(DFT)and its numerical methods,DFT has become a routine method for condensed matter theory,quantum chemistry and material science.In this dissertation,we study a variety of fullerene members and their derivatives,including classical fullerene C₆₀,"missing fullerene"C₇₂and C₇₄,and the unconventional fullerene C₆₄.The concerned properties include the geometric structure, electronic and optical properties.In addition,we also pay attention to the geometric, electronic properties of the Ally Mercaptan(ALM)molecule adsorbed on Si(100)-(2×1) surface.In the first chapter,we introduce the developments of the fullerene as well as the Si surface science.In chapter 2,we introduce the basic concept of DFT and review its recent progress. Finding a good exchange-correlation functional is one of the main targets in DFT.With the development of the modem functionals,from the local density approximation(LDA)and the generalized gradient approximation(GGA)to the more complicated functionals,DFT can obtain more and more accurate results.In addition,along with the development of methods,more and more new program packages have been used to study the properties of materials,thus,we introduce some program packages used usually in the dissertation in detail.In chapter 3 and chapter 4,we focus on the geometric and electronic properties of the Fe substitutional fullerene C₅₈Fe₂ and the Fe endohedral fullerene Fe@C₆₀.The geometric structure research indicates that two Fe prefer to substitute the two carbon atoms of the[6,6] double bond in the most stable C₅₈Fe₂ isomer,while the most favorable endohedral site of Fe is under the center of a hexagon ring in Fe@C₆₀.The electronic property analysis imply that the magnetic moments of Fe and the molecules in both Fe@C₆₀and C₅₈Fe₂ are preserved to some extent though there is hybridization between the Fe and C,in contrast to the completely quenched magnetic moment of the Fe and the molecule in C₅₉Fe.From chapter 5 to chapter 8,we pay our attention to the properties of the "missing fullerene" C₇₂and C₇₄derivatives,i.e,La₂@C₇₂,Si@C₇₄,Ba@C₇₄,and La@C₇₄(C₆H₃Cl₂). In the respect of geometric structure,the La₂@C₇₂(#10611)isomer with the two-fused pentagons is found the most stable,while the most favorable endohedral site of the semiconductor Si is under the center of a pentagon ring on theσ_h plane,while the most favorable endohedral site for both Ba and La in the cage is off-center under the[6,6] double bond along the C₂ axis on theσ_h plane in C₇₄.Concerned to the electronic structure,the Si-C bond in Si@C₇₄contains both covalent and ionic characters.The calculated polarizability componentsα_xx和α_yyof Ba@C₇₄and La@C₇₄are zero.All the La@C₇₄isomers have 1μ_B magnetic moment,while the electronic structure of La@C₇₄ (C₆H₃Cl₂)is closed-shell.In chapter 9 and chapter 10,the structural and electronic properties of the exohedral unconventional fullerene derivatives C₆₄X(X=Si and Ge)and C₆₄X₄(X=H,F,Cl,Br,and I)are tudied.The wave functions of the lowest unoccupied molecular orbital of C₆₄are localized mainly around the triplet-pentagon-fusion,indicated as active sites in chemical reactions,facilitating atom to attach exohedrally.The vertex of the three fused pentagons in the C₆₄cage is confirmed as the most stable position to locate the X atom when four stable isomers of C₆₄X are calculated.The calculated reaction heats of the most stable C₆₄Si and C₆₄Ge isomers are 1.89 and 0.49eV,inferring the reactions to synthesize them are favorable.The frontier orbital theory(FOT)is used to study the possibility for synthesizing C₆₄X.On the other hand,it is discovered from the reactive heats,energy gaps and the largest vibrational frequencies that C₆₄F₄ should be the most stable of five C₆₄X₄ (X=H,F,Cl,Br,and I)molecules,since the less stable C₆₄Cl₄ has been successfully synthesized and isolated,therefore,C₆₄F₄ could be synthesized and isolated experimentally in future.The electronegativity of the fragment C-X of C₆₄X₄(X= F,Cl,Br,and I)is decreased along with the increase of the atom number of X.However,the electronegativity of the fragment C-X in the molecules is affected by the location site.In the last chapter,we focus on the structural and electronic properties of the 0.5ML-terminated ALM/Si(100)-(2×1)surface.The calculated absorption energy of the ALM molecule on the full-terminated H/Si(100)-(2×1)surface is 3.36eV,indicating that the adsorption is favorable in the view of energy.The bottom of the valence band and the top of the conduction band of Si(100)-(2x1),ALM/Si(100)-(2×1)and H/Si(100)-(2×1) are at the different K point,in addition,there is no energy level through the fermi level, therefore,all three surfaces show the indirect semiconductor character.When the ALM molecules are adsorbed on the full-terminated H/Si(100)-(2×1)surface,the band gap is decreased to some degree.Known from both the electron transference and atom orbital hybridizations between the silicon and carbon of the Si-C bond,we come to the conclusion that the ALM molecule should be chemical adsorbed on the H/Si(100)-(2×1)surface...