Thethermodynamicpropertiesofcrystalscanberoutinelycalculatedbydensityfunctionaltheorycalculationscombiningwithquasi-harmonicapproximation.BasedonthemethoddevelopedrecentlybyWuandWentzcovitch(PhysRevB79:104304,2009)andWu(PhysRevB81:172301,2010),weareabletofurtherabinitioincludeanharmoniceffectonthermodynamicpropertiesofcrystalsbyoneadditionalcanonicalensemblewithnumbersofparticle,volumeandtemperaturefixed(NVT)moleculardynamicsimulations.Ourstudyindicatesthatphonon–phononinteractioncausestherenormalizedphononfrequenciesofwadsleyitedecreasewithtemperature.ThisisconsistentwiththeRamanexperimentalobservation.TheanharmonicfreeenergyofwadsleyiteisnegativeanditsheatcapacityatconstantpressurecanexceedtheDulong–Petitlimitathightemperature.Theanharmonicitystillsignificantlyaffectsthermodynamicpropertiesofwadsleyiteatpressureandtemperatureconditionscorrespondtothetransitionzone.
