Bicyclic digraphs with maximal energy

If D is a digraph with n vertices then the energy of D   is defined as E(D)=∑k=1n|Re(zk)|, where Re (z1),…,(z1),…, Re(zn  ) are the real parts of the eigenvalues z1,…,znz1,…,zn of D  . In this paper we solve a problem proposed in Khan et al. (2015), we find the maximal value of the energy over the set of all bicyclic digraphs BnBn with n vertices.