The local charge distributions of different shape graphene sheets are investigated by using the quantum calculations. It is found that the charge distribution on carbon atom is not uniform, strongly depending on its position in the graphene and its local atomic environment condition. The symmetrical characteristic and geometrical structures of graphene also have an important influence on the charge distribution. The charges of atom at the graphene edge are strongly related to their surrounding bonds. It is found that the charges of double-bonded atom at the zigzag edge are closely related to the bond angle, but the charges of double-bonded atom at the armchair edge are mainly influenced by the area of triangle. The charges of triple-bonded atom at the edge are mainly affected by the standard deviation of the length of the associated triple bonds.
We used the semi-empirical quantum calculations to simulate the structural evolution of the isolated one-dimensional linear atomic chains of C, Si, S and P in the process of stretching and compression. The effects of stretching or buckling behavior on the charge distribution of C, Si, P and S single atom chains were studied. Our results show that the C and Si atomic chains tend to form stable linear structures, in which the charges are odd-evenly oscillated. For the first time we theoretically predict that S and P atoms can form stable curved chain structures. At the beginning of the elastic compression range, the linear atom chains of C and Si have a metastable transition state, that is, there is a bending point at which the chain's binding energy suddenly reduces a little then increases with further compression. The charges in the chains are locally uneven and symmetrically distributed, and the number of charges fluctuates in the chains. The charge gain or loss of each C or Si atom is stable during compression, while change slightly during stretching.
The atomic sulfur adsorption on the metastable, unreconstructed Ir(100) surface is studied
from density functional theory calculations with two exchange correlation functionals. The fourfold
hollow site is energetically preferred for both the p(2×2) and c(2×2) structures. Based on the most
favored adsorption georemetries, vibrational frequency and work function are also calculated.
Moreover, a detailed comparison is presented between two functional performances.
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