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Assessment of Density Functional Methods for Obtaining Geometries at Conical Intersections in Organic Molecules.

Filatov M - J Chem Theory Comput (2013)

Bottom Line: The minimum energy conical intersections have been optimized for several molecular systems, which are widely used as paradigmatic models of photochemical rearrangements and models of biological chromophores.The results of the calculations are analyzed using the sign-change theorem of Longuet-Higgins and a method of elementary reaction coordinates of Haas et al.Overall, the BH&HLYP density functional yields the best results for the conical intersection geometries and energetics.

View Article: PubMed Central - PubMed

Affiliation: Institut für Physikalische und Theoretische Chemie, Universität Bonn , Beringstr. 4, D-53115 Bonn, Germany.

ABSTRACT
A number of commonly available density functionals have been tested for their ability to describe the energetics and the geometry at conical intersections in connection with the spin-restricted ensemble referenced Kohn-Sham (REKS) method. The minimum energy conical intersections have been optimized for several molecular systems, which are widely used as paradigmatic models of photochemical rearrangements and models of biological chromophores. The results of the calculations are analyzed using the sign-change theorem of Longuet-Higgins and a method of elementary reaction coordinates of Haas et al. The latter approach helps to elucidate the differences between the geometries at conical intersections as predicted by the multireference wave function ab initio methods and by the density functional methods. Overall, the BH&HLYP density functional yields the best results for the conical intersection geometries and energetics.

No MeSH data available.


Potential energy profilesof the S0 and S1 states of PSB3 obtained by arigid scan along the BLA coordinate (in Å) connecting TSCT for the heterolytic C=C bond breaking and MECI usingthe SI-SA-REKS method in connection with various density functionals.The energies (in eV) are given with respect to the ground state equilibriumenergy of cis-PSB3. TSCT is always locatedat the beginning of the potential energy curves corresponding to individualfunctionals.
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fig14: Potential energy profilesof the S0 and S1 states of PSB3 obtained by arigid scan along the BLA coordinate (in Å) connecting TSCT for the heterolytic C=C bond breaking and MECI usingthe SI-SA-REKS method in connection with various density functionals.The energies (in eV) are given with respect to the ground state equilibriumenergy of cis-PSB3. TSCT is always locatedat the beginning of the potential energy curves corresponding to individualfunctionals.

Mentions: Figure 14 shows the S0 and S1 PESs of PSB3 along theBLA pathway connecting TSCT with MECI. The crossing betweenthe PESs occurs on an uphill segmentof the curves and, after the MECI point, no transition state withdiradical character can be found. In the case of the HF energy functional,a possible TSDIR structure may find itself in the nearestproximity of the MECI geometry, and therefore, this transition statecould not be located. The CASSCF and CASPT2 methods both predict thatthe TSCT and TSDIR structures have nearly equalenergies (see Figure 2 in ref (60).) and only the MRSDCImethod puts TSCT considerably below TSDIR.21,60 As a consequence of nearly equal TSCT and TSDIR energies in CASSCF and CASPT2 calculations, the MECI, which occursbetween these structures, has a substantial charge transfer characterand the C=N bond of the ethyliminium fragment possesses a noticeablygreater single bond character as a result of the charge transfer tothis fragment. The SI-SA-REKS calculations predict MECI considerablyfarther away from the TSCT geometry and the MECI geometryhas a more pronounced resemblance of a would-be TSDIR structure.It is noteworthy that the potential energy curves reported in Figure 14 are much closer to the curves obtained using theMRSDCI method.60 However, in the latercase, the CASSCF geometries were employed60 whereas they are optimized in the present work.


Assessment of Density Functional Methods for Obtaining Geometries at Conical Intersections in Organic Molecules.

Filatov M - J Chem Theory Comput (2013)

Potential energy profilesof the S0 and S1 states of PSB3 obtained by arigid scan along the BLA coordinate (in Å) connecting TSCT for the heterolytic C=C bond breaking and MECI usingthe SI-SA-REKS method in connection with various density functionals.The energies (in eV) are given with respect to the ground state equilibriumenergy of cis-PSB3. TSCT is always locatedat the beginning of the potential energy curves corresponding to individualfunctionals.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3794441&req=5

fig14: Potential energy profilesof the S0 and S1 states of PSB3 obtained by arigid scan along the BLA coordinate (in Å) connecting TSCT for the heterolytic C=C bond breaking and MECI usingthe SI-SA-REKS method in connection with various density functionals.The energies (in eV) are given with respect to the ground state equilibriumenergy of cis-PSB3. TSCT is always locatedat the beginning of the potential energy curves corresponding to individualfunctionals.
Mentions: Figure 14 shows the S0 and S1 PESs of PSB3 along theBLA pathway connecting TSCT with MECI. The crossing betweenthe PESs occurs on an uphill segmentof the curves and, after the MECI point, no transition state withdiradical character can be found. In the case of the HF energy functional,a possible TSDIR structure may find itself in the nearestproximity of the MECI geometry, and therefore, this transition statecould not be located. The CASSCF and CASPT2 methods both predict thatthe TSCT and TSDIR structures have nearly equalenergies (see Figure 2 in ref (60).) and only the MRSDCImethod puts TSCT considerably below TSDIR.21,60 As a consequence of nearly equal TSCT and TSDIR energies in CASSCF and CASPT2 calculations, the MECI, which occursbetween these structures, has a substantial charge transfer characterand the C=N bond of the ethyliminium fragment possesses a noticeablygreater single bond character as a result of the charge transfer tothis fragment. The SI-SA-REKS calculations predict MECI considerablyfarther away from the TSCT geometry and the MECI geometryhas a more pronounced resemblance of a would-be TSDIR structure.It is noteworthy that the potential energy curves reported in Figure 14 are much closer to the curves obtained using theMRSDCI method.60 However, in the latercase, the CASSCF geometries were employed60 whereas they are optimized in the present work.

Bottom Line: The minimum energy conical intersections have been optimized for several molecular systems, which are widely used as paradigmatic models of photochemical rearrangements and models of biological chromophores.The results of the calculations are analyzed using the sign-change theorem of Longuet-Higgins and a method of elementary reaction coordinates of Haas et al.Overall, the BH&HLYP density functional yields the best results for the conical intersection geometries and energetics.

View Article: PubMed Central - PubMed

Affiliation: Institut für Physikalische und Theoretische Chemie, Universität Bonn , Beringstr. 4, D-53115 Bonn, Germany.

ABSTRACT
A number of commonly available density functionals have been tested for their ability to describe the energetics and the geometry at conical intersections in connection with the spin-restricted ensemble referenced Kohn-Sham (REKS) method. The minimum energy conical intersections have been optimized for several molecular systems, which are widely used as paradigmatic models of photochemical rearrangements and models of biological chromophores. The results of the calculations are analyzed using the sign-change theorem of Longuet-Higgins and a method of elementary reaction coordinates of Haas et al. The latter approach helps to elucidate the differences between the geometries at conical intersections as predicted by the multireference wave function ab initio methods and by the density functional methods. Overall, the BH&HLYP density functional yields the best results for the conical intersection geometries and energetics.

No MeSH data available.