1. C. Adiga, R. Balakrishnan and W. So, The skew energy of a digraph, Linear Algebra Appl. 432 (2010), 1825-1835.
2. M. A. Bhat, Energy of weighted digraphs, Discrete Appl. Math. 223 (2017) 1-14.
3. D. M. CvetkoviÄ‡, M. Doob and H. Sachs, Spectra of Graphs: Theory and Application, third revised and enlarged edition, J. A. Barth Verlag, Heidelberg-Leipzig, 1995.
4. R. Farooq, M. Khan and S. Chand, On iota energy of signed digraphs, Linear Multilinear Algebra 67 (4) (2019) 705-724.
5. R. Farooq, M. Khan and F. Ahmad, Extremal iota energy of bicyclic digraphs, Appl. Math. Comput. 303 (2017) 24-33.
6. I. Gutman, The energy of a graph, Ber. Math. Stat. Sekt. Forschungszentrum Graz 103 (1978) 1-22.
7. I. Gutman and X. Li (Eds.), Energies of Graphs - Theory and Applications, University of Kragujevac, Kragujevac, 2016.
8. M. Khan, R. Farooq and A. A. Siddiqui, On the extremal energy of bicyclic digraphs, J. Math. Inequal. 9 (3) (2015) 799–810.
9. M. Khan, R. Farooq and J. Rada, Complex adjacency matrix and energy of digraphs, Linear Multilinear Algebra 65 (11) (2017) 2170–2186.
10. W. Lopez and J. Rada, Equienergetic digraphs, Int. J. Pure Appl. Math. 36 (3) (2007) 361-372.
11. J. Monsalve, J. Rada and Y. Shi, Extremal values of energy over oriented bicyclic graphs, Appl. Math. Compt. 342 (2019), 26-34.
12. I. Pena and J. Rada, Energy of digraphs, Linear Multilinear Algebra 56 (5) (2008) 565-579.
13. J. Rada, The McClelland inequality for the energy of digraphs, Linear Algebra Appl. 430 (2009) 800-804.