The institute's good performance in the ranking is mainly due to PIK's Chief Economist Ottmar Edenhofer. He counts as - in the paper's terms - an "influential economist" not just because he authored numerous much-quoted studies, but also because of his role as co-chair of the Working Group III Climate Change Mitigation of the IPCC, the Intergovernmental Panel on Climate Change. In the ranking of German universities with top economists, the Technische Universität Berlin achieved second place, partly due to the fact that Edenhofer is a professor there. He has already previously been ranked as one of the most important German economics researchers.
Weblink to the ranking (German only): http://www.faz.net/aktuell/wirtschaft/wirtschaftswissen/f-a-z-oekonomenranking-2014-lmu-und-diw-gewinnen-13190827.html