Removing the extra frontier parameters in QM/MM methods: a tentative with the Local Self-Consistent Field method

We present a new quantum mechanics/molecular mechanics (QM/MM) scheme based on the Local-SCF method that avoids the extra-parametrization of the QM/MM frontier by taking into account the core electrons of the hybrid frontier atoms by means of self-consistent core orbitals (SCCO). This study follows and extends our previous investigation based on frozen core orbitals (FCO) [Chem. Phys. Lett. 427 236-240(2006)]. Test calculations on small organic compounds show that the most common atoms found in biochemical systems can be used as frontier atoms without adding any parameters, and that only relatively small geometric and energetic deviations compared to full-QM calculations are generated.