Structures and energetics of Si3N2 clusters

Abstract

Aglomerados mistos de silício e nitrogênio com fórmula Si 3 N 2 foram investigados teoricamente com os métodos SCF e MP2. Dos onze pontos estacionários encontrados abaixo de 80 kcal/mol, oito correspondem a mínimos locais (ML); desses, cinco são estados singletos. Quanto aos tripletos, três ML e um estado de transição (ET) foram caracterizados. O mínimo global corresponde a uma estrutura angular com ligações alternadas silício-nitrogênio, que contrasta com as estruturas lineares de outros aglomerados menores de Si/N. Uma estrutura bipiramidal mais alta em energia 41.0 kcal/mol pode ser vista como um padrão natural para um crescimento tridimensional. Em geral, estruturas com mais ligações SiN são preferidas energeticamente em relação àquelas em que as ligações SiSi predominam. Tentativas para se localizar ET que se correlacionam com os canais de dissociação mais baixos não tiveram sucesso devido à complexa e computacionalmente difícil busca. Apesar disso, garante-se a estabilidade termodinâmica das estruturas I, III, IV e V, sendo a energia do canal mais baixo um limite inferior. A energia de atomização da estrutura do mínimo global é de 420.6 kcal/mol (MP2).Mixed clusters of silicon and nitrogen with formula Si 3 N 2 have been investigated at both SCF and MP2 levels of theory. Of eleven stationary points found below 80 kcal/mol, eight correspond to local minima (LM); of these, five are singlet states. Of the triplets, three LM and one transition state (TS) were characterized. The global minimum corresponds to an angular structure with alternating siliconnitrogen bonds, in contrast with linear ones for other smaller Si/N clusters. A bipyramidal structure 41.0 kcal/mol high in energy can be seen as a natural pattern for tridimensional growing. In general, structures with more SiN bonds are energetically preferred to those in which the SiSi bonds predominate. Attempts to locate TS correlating with the lowest dissociation channels have been unsuccessful due the complex and computationally demanding search. Despite this fact, the thermodynamic stability for structures I, III, IV, and V is guaranteed, being the energy of the lowest channel a lower bound. The atomization energy for the global minimum structure amounts to 420.6 kcal/mol (MP2).

Structure and Stability of M6N8 Clusters (M = Si, Ge, Sn, Ti)

“…The formation and properties of small Si-N species such as SiN, Si 2 N, SiN 2 , Si 2 N 2 , Si 3 N 4 , and others have been extensively investigated both experimentally [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretically. 11, [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] In contrast, research about larger clusters is limited. Joseph et al 35 studied the high temperature behavior of Si 3 N 4 using laser-induced vaporization mass spectrometry, where they observed not only gaseous Si 3 N 4 but also Si 6 N 8 species.…”

“…In this context, considerable attention has been given to gaseous silicon−nitrogen clusters. The formation and properties of small Si−N species such as SiN, Si 2 N, SiN 2 , Si 2 N 2 , Si 3 N 4 , and others have been extensively investigated both experimentally − and theoretically. ,− In contrast, research about larger clusters is limited. Joseph et al studied the high temperature behavior of Si 3 N 4 using laser-induced vaporization mass spectrometry, where they observed not only gaseous Si 3 N 4 but also Si 6 N 8 species.…”