In 1981-1984 he was a research assistant, and in 1984-1986 an assistant professor, at the Faculty of Chemistry of Sofia University. In 1986 he moved to the Institute of Organic Chemistry of the Bulgarian Academy of Sciences, where he was a research fellow until 1994. In 1990-1995 he was a visiting research associate with Joe Gerratt at the School of Chemistry of the University of Bristol, and in 1995-2001 a lecturer in physical & computer-aided chemistry at the Department of Chemistry of the University of Surrey. Since May 2001 PBK is a reader in theoretical chemistry at the Department of Chemistry of the University of York.
PBK's research interests are in molecular electronic structure theory.