期刊
JOURNAL OF CHEMICAL PHYSICS
卷 135, 期 20, 页码 -出版社
AIP Publishing
DOI: 10.1063/1.3663856
关键词
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资金
- AFOSR through the COMAS MURI [FA9550-10-1-0558]
- Alexander-von-Humboldt Foundation
Long-range corrected (range-separated hybrid) functionals represent a relatively new class of functionals for generalized Kohn-Sham theory that have proven to be very successful, for instance, when it comes to predicting ionization potentials and energy gaps for a wide range of molecules and solids. The results obtained from long-range corrected density functional theory approaches can be improved dramatically, if the range-separation parameter (omega) is optimized for each system separately. In this work, we have optimized omega for a series of pi-conjugated molecular systems of increasing length by forcing the resulting functionals to obey the ionization potential-theorem, i.e., that their highest occupied eigenvalue be equal to the Delta SCF ionization potential. The optimized omega values are observed to vary substantially from their default values for the functionals. For highly conjugated chains such as oligoacenes and polyenes, we find that the characteristic length scale of the range-separation, i.e., 1/omega, grows almost linearly with the number of repeat units, for saturated alkane chains, however, 1/omega quickly saturates after 5-6 repeat units. For oligothiophenes, we find that 1/omega grows linearly for the shorter oligomers but then saturates at around 10 repeat units. Our results point to a close relation between the optimal range-separation parameter and the degree of conjugation in the system. (C) 2011 American Institute of Physics. [doi:10.1063/1.3663856]
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