|The Born-Oppenheimer approximation (BOA) is one the most fundamental approximations of molecular physics and chemistry. This approximation has been used successfully in many research areas ranging from spectroscopy to quantum chemistry. In fact, the use of this approximation in quantum chemistry has made possible the study of molecular systems containing thousands of electrons and nuclei. However, quantum chemistry methods based on the BOA still fail to include nuclear quantum effects (NQE) on the molecular electronic structure, because the BOA completely uncouples the electronic and nuclear degrees of freedom. For most chemical systems these effects beyond the BOA are very small. However, for systems containing light or delocalized nuclei, they may be very important.
LOWDIN software package has resulted from the merging of the Any Particle Molecular Orbital (APMO) [developed at the Reyes' group at Universidad Nacional, Colombia] and PARAKATA software [developed at the Flores-Moreno group at Universidad de Guadalajara, Mexico] packages to study phenomena beyond the BOA. LOWDIN implements the Any Particle Molecular Orbital method at the Hartree-Fock (RHF, UHF and ROHF), Moller-Plesset (MP2), and Density Functional (DFT) levels of theory. In addition, LOWDIN implements the electronic and nuclear propagator and auxiliary density perturbation theory methods.
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