F Afshar - Department of Science, Garmsar Brunch, Islamic Azad University, Garmsar, Iran
F Ghaziani - Faculty of Agricultural Engineering, University of Tehran, Karaj, Iran

Formation of polymorphs is important phenomenon because of their different pharmaceuticalproperties [1] and many drugs receive regulatory approval for only a single crystal form orpolymorph. An illustrious sample of polymorphism effect on real pharmaceutical problems isthe ritonavir (an important AIDS drug), the Abbott compound [2]. Ab initio studies are ofgreat interest in recent years because of its ability to obtain a variety of important molecularquantities such as electron density distribution, reactivity, structure, and energy [3]. In thiswork, Ab initio calculations were performed to optimize two different structures(polymorphs), a and b, of a carbacylamidophosphate, 4-NC5H4C(O)NHP(O)[NH–C(CH3)3]2.