Grigory Shamov - Stability of Hydrocarbons of the Polyhedrane Family Containing Bridged CH Groups: A Case of Failure of the Colle−Salvetti Correlation Density Functionals

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  J. Chem. Theory Comput., 2010,   6 (11), pp 3442–3455
  Publication Date (Web): October 22, 2010   (Article)
  DOI: 10.1021/ct100389d


  DFT-computed energies of polyhedric hydrocarbons, such as   dodecahedrane C20H20, its smaller analogs   C16H16 and C12H12,   and the larger C24H24,  estimated in   comparison with corresponding isomeric hydrocarbons, vary    widely with the choice of the density functional. In particular,   large  discrepancies were observed with the functionals that   are based on the  B88 (as well as G96, B86) exchange and the   LYP (as well as OP)  correlation parts. The problem is not   related to the presence of the  smaller cyclopropane rings   in the C12H12 polyhedrane, for its   hydrogenated products do show similar errors;  moreover, the   larger dodecahedrane that is free from the Bayer strain    shows a similar trend. DFT-D corrections that are very useful in   fixing  long- and medium-range correlation issues with GGA   DFT do not help in  this case either. We show that these   errors stem from the B88 (G96, B86)  exchange functionals   and are not compensated by Colle−Salvetti-based  GGA   correlation functionals such as LYP, OP, TCA, etc. However, they   can  be corrected by the PBE correlation functional based on   the PW92  uniform electron gas (UEG) parametrization.   Range-separated hybrids  (Iikura and Hirao’s LC-BOP,   LC-BLYP) perform much better than the parent  GGAs.   Comparisons of polyhedranes with a well-studied system of   similar  size, the set of   CnHn cyclophanes,    reveal a completely different performance for the latter—for   instance,  RHF results are the poorest, and LC-type   functionals do not give any  improvement, but   dispersion-corrected BLYP-D performs very well. We  conclude   that, while for polyhedranes medium-range delocalization   errors  from exchange dominate, for cyclophanes, the    correlation/overlap-dispersion interactions are more important.   The OPTX  exchange functional shows significantly lower   errors compared to B88  and G96; its combinations like OLYP   and especially KT3 perform well for  both test sets. The   OPTX-based double hybrid, O2PLYP, also outperforms  the   corresponding B88-based B2PLYP functional for polyhedranes.   Our  computations also suggest that the (CH)16  and (CH)24 polyhedranes could be possible synthetic   targets.

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