Quantum Mechanical Force Field QMFF

In the following sections, we summarize the theoretical formulation of the X-Pol model and illustrate the multilevel X-Pol method for studying intermolecular interactions. In addition, we discuss our work on using X-Pol as a quantum mechanical force field (QMFF) for liquid water simulations. 

CFF = consistent force field QMFF = quantum mechanical force field. 

The consistent force field (CFF) was developed to yield consistent accuracy of results for conformations, vibrational spectra, strain energy, and vibrational enthalpy of proteins. There are several variations on this, such as the Ure-Bradley version (UBCFF), a valence version (CVFF), and Lynghy CFF. The quantum mechanically parameterized force field (QMFF) was parameterized from ah initio results. CFF93 is a rescaling of QMFF to reproduce experimental results. These force fields use five to six valence terms, one of which is an electrostatic term, and four to six cross terms. 

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