The lack of reference aromatic systems in the realm of inorganic aromatic compounds makes the evaluation of aromaticity in all-metal and semimetal clusters a difficult task. To date, calculation of nucleus-independent chemical shifts (NICS) has been the most widely used method to discuss aromaticity in these systems. In the first part of this work, we briefly review our previous studies, showing some pitfalls of the NICS indicator of aromaticity in organic molecules. Then, we refer to our study on the performance of some aromaticity indices in a series of 15 aromaticity tests, which can be used to analyze the advantages and drawbacks of aromaticity descriptors. It is shown that indices based on the study of electron delocalization are the most accurate among those analyzed in the series of proposed tests, while NICS(1)zz and NICS(0)pzz present the best behavior among NICS indices. In the second part, we discuss the use of NICS and electronic multicenter indices (MCI) in inorganic clusters. In particular, we evaluate the aromaticity of two series of all-metal and semimetal clusters with predictable aromaticity trends by means of NICS and MCI. Results show that the expected trends are generally better reproduced by MCI than NICS. It is concluded that NICS(0)p and NICS(0)pzz are the kind of NICS that perform the best among the different NICS indices analyzed for the studied series of inorganic compounds

Financial help has been furnished by the Spanish MICINN Project No. CTQ2008-03077/BQU and by the Catalan DIUE through project No. 2009SGR637. F.F. and J.P. thank the MICINN for the doctoral fellowship No. AP2005-2997 and the Ramon y Cajal contract, respectively. E. M. acknowledges financial support from the Lundbeck Foundation Center and from Marie Curie IntraEuropean Fellowship, Seventh Framework Programme (FP7/2007-2013), under grant agreement No. PIEF-GA-2008-221734 and from the Polish Ministry of Science and Higher Education (Project No. N N204 215634). Support for the research of M. S. was received through the prize "ICREA Academia" 2009 for excellence in research funded by the DIUE of the Generalitat de Catalunya. We thank the Centre de Supercomputacio de Catalunya (CESCA) for partial funding of computer time