Abstract: Based on the recent theory of built-in potential [1], we develop a scheme for intrinsic band alignment where the vacuum-level position in an infinite solid can be identified and used as the common energy reference among dissimilar bulk materials [2]. Unique to this theory is the recognition of an orientation dependence of bulk energies with respect to the vacuum due to bulk quadrupole – a quantity that can now be unambiguously evaluated. It reveals that the long-pursued concept of a universal band alignment is ill-defined because of the orientation-dependent quadrupole. This information lays solid ground for understanding intrinsic band alignment with respect to vacuum, which is vitally important for practical applications ranging from solid-state band offset, electrochemical potential of a cell, to redox potential in electrochemistry.Work was in collaboration with Choe and West and supported by US DOE under Grant No. DE-SC0002623. [1] D.-H. Choe, D. West, and S. Zhang, Phys. Rev. Lett. 121, 196802 (2018). [2] D.-H. Choe, D. West, and S. Zhang, arXiv:1906.10162. . About the speaker: Prof Shengbai Zhang received his Ph. D. in Physics from the University of California at Berkeley in 1989 under the supervision of Professor Marvin L. Cohen. Dr. Zhang then joined Xerox PARC in Palo Alto California where he performed postdoctoral research with Dr. Jim Chadi and Dr. John Northrup. In 1991 he moved to the National Renewable Energy Laboratory (NREL) in Golden Colorado and became group leader for Computational Materials Science in 2005. In 2008 he was appointed Senior Kodosky Constellation Chair at Rensselaer Polytechnic Institute in Troy NY. Prof. Zhang has a broad theoretical research background in computational materials physics which covers a range of inorganic and organic semiconductors and solids for bulk properties defect structures and surface physics. His most recent work involves earth-abundant photovoltaic materials phase change memory materials van der Waals interaction in organic semiconductors lithium battery materials hydrogen storage topological insulators graphene and excited state dynamics. Dr. Zhang has more than 309 peer-reviewed publications with more than 19000 citations (H index = 69). He has been a Fellow of the American Physical Society since 2001. | 
