Chemical Physics Letters, Vol.456, No.1-3, 76-79, 2008
Theoretical studies on the structure and effective exchange integral (J(ab)) of an active site in oxyhemocyanin (oxyHc) by using approximately spin-projected geometry optimization (AP-opt) method
The effect of a spin contamination error in an optimized geometry of Cu2O2 in the active site of oxyHc is examined by using broken-symmetry (BS) and AP-opt methods with hybrid density functional methods. The error was 3-5 degrees on the Cu-O-Cu angle and 0.07-0.13 angstrom on the reaction coordinate R. The error in the optimized structure strongly affects the calculated Jab values such as 196 and 553 cm(-1) for UBHandHLYP and UB3LYP methods, respectively. The underestimated Jab value of UB3LYP becomes close to the experimental one by the correction of the structure with the AP-opt method. (C) 2008 Elsevier B.V. All rights reserved.