Computational Strategy for Graphene: Insight from Odd Electrons Correlation

The correlation of odd electrons in graphene turns out to be significant so that the species should be attributed to correlated ones. This finding profoundly influences the computational strategy addressing it to multireference computational schemes. Owing to serious problems related to the schemes realization, a compromise can be suggested by using single-determinant approaches based on either Hartree-Fock or Density-Functional theory in the form of unrestricted open-shell presentation. Both computational schemes enable to fix the electron correlation, while only the Hartree-Fock theory suggests a set of quantities to be calculated that can quantitatively characterize the electron correlation and be used for a quantitative description of such graphene properties as magnetism, chemical reactivity, and mechanical response. The paper presents concepts and algorithms of the unrestricted Hartree-Fock theory applied for the consideration of magnetic properties of nanographenes, their chemical modification by the example of stepwise hydrogenation, as well as a possible governing the electron correlation by the carbon skeleton deformation.Comment: 17 pages, 11 figures, 3 table

Stretching and breaking of chemical bonds, correlation of electrons, and radical properties of covalent species

Chemical bonds are considered in light of correlation of valence electrons that is strengthened when the bond is dissociated. In the framework of the unrestricted Hartree-Fock single-reference version of the configuration interaction theory, effectively unpaired electrons lay the foundation of the electron correlation measure in terms of total number of the electrons (molecular chemical susceptibility). graphs and their singularities with respect to the interatomic distance allow presenting a quantitative description of stretching and breaking of chemical bonds. The approach validity is demonstrated on a large number of bonds of different order and chemical composition.Comment: 24 pages, 17 figures, 4 tables, Advances in Quantum Chemistry, vol. 70, 201

Comment on ``Magnon wave forms in the presence of a soliton in two--dimensional antiferromagnets with a staggered field''

Very recently Fonseca and Pires [Phys. Rev. B 73, 012403(2006)] have studied the soliton--magnon scattering for the isotropic antiferromagnet and calculated ``exact'' phase shifts, which were compared with the ones obtained by the Born approximation. In this Comment we correct both the soliton and magnon solutions and point out the way how to study correctly the scattering problem.Comment: 2 pages (RevTeX