fixphonon：对于声子评价LAMMPS的延伸

This project presents an implementation of the method to evaluate the phonon dispersion directly from molecular dynamics simulations. The basic algorithm is to construct the dynamical matrices by observing the displacement fluctuations. For details, check the documents of the project. The implemented method enables one to evaluate the phonon dispersion under finite temperature/pressures without turning to the usual quasi-harmonic procedure. The code presented here needs to work along with LAMMPS, an open-source molecular dynamics simulation package; it is designed as a user-contributed package to LAMMPS, thus making use of the features from LAMMPS. A post-processing code is also provided, helping to analyze the result, which is written as binary files by fix-phonon. External libraries CLapack, Tricubic, and/or