The thesis is divided into two parts.In the first part a global optimization method is developed for the interface and surface structures optimization. Two prototype systems are chosen to be studied. One is Si[001] symmetric tilted grain boundaries and the other is Ag/Au induced Si(111) surface. It is found that Genetic Algorithm is very efficient in finding lowest energy structures in both cases. Not only existing structures in the experiments can be reproduced, but also many new structures can be predicted using Genetic Algorithm. Thus it is shown that Genetic Algorithm is a extremely powerful tool for the material structures predictions. The second part of the thesis is devoted to the

explanation of an experimental observation of thermal radiation from

three-dimensional tungsten photonic crystal structures. The

experimental results seems astounding and confusing, yet the

theoretical models in the paper revealed the physics insight behind

the phenomena and can well reproduced the experimental results.