A programmable optimization environment using the GAMESS-US and MERLIN/MCL packages. Applications on intermolecular interaction energies Original Research Article

The Merlin/MCL optimization environment and the GAMESS-US package were combined so as to offer an extended and efficient quantum chemistry optimization system, capable of implementing complex optimization strategies for generic molecular modeling problems. A communication and data exchange interface was established between the two packages exploiting all Merlin features such as multiple optimizers, box constraints, user extensions and a high level programming language. An important feature of the interface is its ability to perform dimer computations by eliminating the basis set superposition error using the counterpoise (CP) method of Boys and Bernardi. Furthermore it offers CP-corrected geometry optimizations using analytic derivatives. The unified optimization environment was applied to construct portions of the intermolecular potential energy surface of the weakly bound H-bonded complex C6H6–H2O by utilizing the high level Merlin Control Language. The H-bonded dimer HF–H2O was also studied by CP-corrected geometry optimization. The ab initio electronic structure energies were calculated using the 6-31G** basis set at the Restricted Hartree–Fock and second-order Moller–Plesset levels, while all geometry optimizations were carried out using a quasi-Newton algorithm provided by Merlin.