3 Acknowledgements

My supervisor, Prof. Artem R. Oganov, devoted tremendous efforts in guiding, supporting and inspiring me throughout my PhD study. He has made my PhD experience both enjoyable and complete. I am grateful for those exciting discussions with people in my group including Andriy O. Lyakhov, Salah E. Boulfelfel, Yu Xie, Qingfeng Zeng, Chaohao Hu, Guangrui Qian, Xiangfeng Zhou and Xiao Dong. I also want to thank the whole department of Geosciences in Stony Brook, especially Yu Chen, Wenqian Xu and Wei Li, who help me a lot in both science and personal life. Prof. Philip B. Allen and his former PhD student Li Li are also acknowledged for our enjoyable collaboration on surface structure prediction.

I also thank my collegues who are the coauthors of my papers (including Miguel A. Salvado and Pilar Pertierra, Carlo Gatti, Daniel Jung, Colin Glass, Harold T. Stokes) and others for insightful scientific discussions (Gilles Frapper, Julian Gale, Alberto Garcia, Jose Perez and many others).

Prof. John Parise, Prof. Donald Weidner, Prof. Richard Reeder, Prof. Esther Takeuchi and Prof. Mark Tuckman are acknowledged for serving on my thesis defense committee.

I am grateful to my old friends Luowei Cao, Jie Ren, Xiaoping Liu, Xiaoxiang Yu, Yu Zou, Penghao Xiao for friendship, discussions and supports.

This thesis is dedicated to my parents and my wife for their continuous support in my life. I really appreciate everything they have done for me.

Calculations were performed at Blue Gene supercomputer at New York Center for Computational Sciences (Stony Brook University / Brookhaven National Laboratory), and the Joint Supercomputer Center of the Russian Academy of Sciences (Moscow). The work was supported by DARPA (grant N66001-10-1-4037 and W31P4Q1210008) and National Science Foundation (grant EAR-1114313).

The text of this thesis contains materials which have been previously published, in press, under reivew or in submission in the following articles.

Q. Zhu, A. R. Oganov, et al. (2011) Denser than diamond: Ab initio search for superdense carbon allotropes. Phys. Rev. B, 83, 193410

Q. Zhu, A. R. Oganov, A. O. Lyakhov (2012) Evolutionary metadynamics: A novel method to predict crystal Structures. CrystEngComm, 14, 3596–3601

Q. Zhu, A. R. Oganov, et al. (2012) Constrained evolutionary algorithm for structure prediction of molecular crystals: methodology and applications. Acta Cryst. B, 68, 215-226

Q. Zhu, Q. Zeng, A. R. Oganov (2012) Systematic search for low-enthalpy $sp^3$ carbon allotropes using evolutionary metadynamics. Phys. Rev. B, 85, 201407

X-F. Zhou, A. R. Oganov, G-R. Qian, Q. Zhu (2012) First-Principles Determination of the Structure of Magnesium Borohydride. Phys. Rev. Lett., 109, 245503

S. E. Boulfelfel, Q. Zhu, A. R. Oganov, Novel sp$^3$-forms of carbon predicted by evolutionary metadynamics and analysis of their synthesizability using transition path sampling. J. Superhard Mater., 34, 350-359, 2012,

Q. Zhu, et al. (2013) Stability of xenon oxides at high pressures. Nature Chemistry, 5, 61-65

A. O. Lyahkov, A. R. Oganov, H. T. Stokes, Q. Zhu, (2013) New developments in evolutionary structure prediction algorithm USPEX. Comp. Phys. Comm., 184, 1172-1182

Q. Zhu, A. R. Oganov, A. O. Lyahkov, Unexpected Stoichiometries in Mg-O system under high pressure. Phys. Chem. Chem. Phys, 2013, DOI: 10.1039/c3cp50678a

W. Zhang, A. R. Oganov, A. F. Goncharov, Q. Zhu, S. E. Boulfelfel, A. O. Lyahkov, M. Somayazuluand V. B. Prakapenka. Unexpected Stable Stoichiometries of Sodium Chlorides. Science, 2012, under review

C-H. Hu, A. R. Oganov, Q. Zhu, G-R. Qian, G. Frapper, A. O. Lyakhov, and H-Y. Zhou, (2013) Pressure-induced stabilization and insulator-superconductor transition of BH. Phys. Rev. Lett., 2013, Accepted

Q. Zhu, L. Li, A. R. Oganov, P. B. Allen, Evolutionary Method for Predicting Surface Reconstructions with Variable Stoichiometry. Phys. Rev. B, 2013, Under review