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Change of the frontier electronic orbitals due to substitutional impurities in large chemical or biological molecules
Author(s) -
Ren Shang Yuan,
Dow John D.
Publication year - 1990
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560381710
Subject(s) - homo/lumo , molecular orbital , impurity , atomic orbital , chemistry , anderson impurity model , band gap , magnetic impurity , electronic structure , atomic physics , molecule , computational chemistry , chemical physics , condensed matter physics , physics , electron , quantum mechanics , organic chemistry
Abstract A molecule whose electronic structures are poorly understood, in some cases, can be thought of as another perhaps well‐understood “host chemical molecule” with substitutional “impurities.” From this point of view, the Green's function technique in solid state physics can be extended to investigate the change due to substitutional impurities in large chemical or biological molecules of the frontier electronic orbitals—the highest occupied molecular orbitals ( HOMO ) and the lowest unoccupied molecular orbitals ( LUMO ). These orbitals are the ones most active in chemical reactions, and are conceptually very similar to the valence band and conduction band states of semiconductors. Substitutional impurities will often introduce new “deep” electronic states into the gap between the HOMO and LUMO states of the original molecule and these states will have the following properties. ( i ) The likelihood that an impurity will produce a state in the gap depends on the site of the impurity. ( ii ) For impurities on a particular site, the wavefunction of the gap state will be relatively independent of the impurity. ( iii ) Only a small fraction of the deep level wavefunction (typically 10%) will lie within the impurity's cell and the largest part (about 40–50%) will be on the impurity's nearest‐neighbor atoms. ( iv ) The derivative of the energy of the impurity state with respect to the central‐cell impurity potential dE/dV is approximately equal to the probability of the gap‐state electron being found on the impurity's site.