Program Structure
The program is built of two modules: crystal and properties. The crystal program is dedicated to perform the SCF calculations, the geometry optimizations, and the frequency calculations for the structures given in input. At the end of the SCF process, the program crystal writes information on the crystalline system and its wave function as unformatted sequential data in Fortran unit 9, and as formatted data in Fortran unit 98. One-electron properties and wave function analysis can be computed from the SCF wave function by running the program properties.
The main advantage of the crystal code is due to the deep and optimized exploitation of symmetry, at all levels of calculation (SCF as well gradients and vibrational frequencies calculations). This allows significant reduction of the computational cost for periodic calculations. Note that while the symmetry generally reduces to identity in large molecules, large crystalline system usually show many symmetry operators.
Read more about this topic: Crystal (software)
Famous quotes containing the words program and/or structure:
“It is said the city was spared a golden-oak period because its residents, lacking money to buy the popular atrocities of the nineties, necessarily clung to their rosewood and mahogany.”
—Administration in the State of Sout, U.S. public relief program (1935-1943)
“The structure was designed by an old sea captain who believed that the world would end in a flood. He built a home in the traditional shape of the Ark, inverted, with the roof forming the hull of the proposed vessel. The builder expected that the deluge would cause the house to topple and then reverse itself, floating away on its roof until it should land on some new Ararat.”
—For the State of New Jersey, U.S. public relief program (1935-1943)