Semi-empirical electronic structure method advantages

About 25 years ago experimental and theoretical studies of molecular structures and conformational properties were done quite separately. Because theoretical methods have also become applicable for reasonably sized molecules, experimental investigators started to take advantage of these methods and included molecular mechanics (MM), semi-empirical, and later ab initio and/or density flmctional (DFT) calculations in their experimental analyses. Today, because computer programs are very easy to use and sufficient computer capacity is generally available, most experimental studies of gas phase structures by gas electron diffraction (GED), microwave (MW), or high-resolution infrared spectroscopy are combined with theoretical calculations. 

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