Modified carbon pseudopotential for use in ONIOM calculations of alkyl-substituted metallocenes

Nonrelativistic carbon 1s core pseudopotentials are optimized for substituted cyclopentadienide ring carbons for use in integrated molecular orbital molecular orbital (IMOMO) and integrated molecular orbital molecular mechanics (IMOMM) calculations where the Cp ring substituents are not included in the high-level IMOMO or IMOMM subsystem. Use of the optimized pseudopotential within the IMOMO framework leads to significant improvements in predicted carbonyl stretching frequencies for a series of Cp-ring-methylated zirconocenes compared to using a standard carbon pseudopotential. The technology is less successful in the IMOMM implementation.