Topic: Exploring structures and phase relationships of ceramics at finite temperatures from first principles

Speaker: Prof. Isao Tanaka

Department of Materials Science and Engineering

Kyoto University, Japan

Abstract:

First principles calculations on the basis of density functionaltheory (DFT) have been developed over thelast few decades. Progress of computational powers and techniquesis remarkable during this period. Crystals with severalhundreds of atoms can be routinely examined by the DFTmethods using personal computers these days. When clusteredcomputers are employed, DFT calculations of periodic unitscomposed of several thousands of atoms can be done withoutmuch technical difficulties. Today one can also perform a largeset of DFT calculations systematically with high numericalaccuracy. Capability of a large set of calculations is often moreimportant in materials science community than a large sizecalculation, since the information can be used to evaluatethermodynamical quantities. When statistical thermodynamics iscombined with a systematic set of first principles calculations, theconfigurational and vibrational contributions to thermodynamicalquantities and their temperature dependence can beevaluated. When phonon states are obtained, the products andpathways of phase transitions can also be analyzed on the basisof the information of imaginary phonon modes. Such theoreticalresults can not only "reproduce" available experimental data butalso "predict" as-yet-unknown structures and properties. Evenwhen experimental data were reported, they are sometimeswidely scattered or conflicting. Then theoretical calculations canbe used to adjudicate upon the arguments. In this lectureI showmany examples how we use DFT methods in conjunction withlattice dynamics and statistical thermodynamics simulations toelucidate structures and phase relationships ofselected ceramic materials.