Dear Sadeqh,
CAM-B3LYP combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al. CAM-B3LYP yields atomization energies of similar quality to those from B3LYP, while also performing well for charge transfer excitations in a dipeptide model, which B3LYP underestimates enormously. The CAM-B3LYP functional comprises of 0.19 Hartree–Fock (HF) plus 0.81 Becke 1988 (B88) exchange interaction at short-range, and 0.65 HF plus 0.35 B88 at long-range. The intermediate region is smoothly described through the standard error function with parameter 0.33.
B3LYP – probably the most successful functional so far.
it has a number of deficiencies:
polarizabilities of long chains.
excitation using TD-DFT for Rydberg states.
charge transfer (CT) excitations.
Reasons understood: long range exchange potential
behaves like −0.2r−1 instead of −r−1
.
CAM-B3LYP is meant to address these deficiencies.
Normalized alkene polarizabilities as a function of chain length.
CAM-B3LYP gets the trend right (close to HF). LDA too steep. B3LYP is
in the middle.
Model ethylene - tetrafluoroethylene system.
Fact: CT excitation energy varies like −R−1
.
CAM-B3LYP gives CT state with a correct trend.
LDA (SVN5) cannot describe nonlocal excitations properly.
GGA (BLYP) does not improve on it.
CAM-B3LYP provides much better estimation of non-local excitation energy
G2 test set (short bonds): CAM-B3LYP ≈ B3LYP
CAM-B3LYP improves long-range interactions: better
description of molecules with long bonds and reaction barriers.
CAM-B3LYP: a improvement on the long-range-corrected
(LC) exchange functional of Yanai.
provides as accurate description of charge-transfer systems
as LC. . .
. . . without sacrifying other properties (atomization energies).
For more information, please use the following link:
https://www.theochem.kth.se/courses/acm3/part1/lecture-7.pdf
Hoping this will be helpful,
Rafik
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