Vol.:(0123456789) 1 3 Applied Nanoscience https://doi.org/10.1007/s13204-018-0859-9 REVIEW ARTICLE Comparison of experimental and frst-principle results of band-gap narrowing of MgO nanostructures and their dependence on crystal structural parameters N. Kamarulzaman 1,2  · D. T. Mustafa 1,2  · N. F. Chayed 1,2  · N. Badar 1,2  · M. F. M. Taib 2  · A. B. M. A. Ibrahim 2 Received: 25 June 2018 / Accepted: 13 August 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract From experimental investigations of the bandgaps of magnesium oxide (MgO) nanostructures, the results show that band-gap narrowing occurred as the physical dimension of the MgO crystallites decrease. This is in contrast to other metal oxides such as ZnO. To obtain insights on this observed phenomenon, the frst-principle studies using density functional theory were carried out. The strategy used here is diferent from the normal theoretical studies, such that information of the structural characterization obtained from experimental X-ray difraction (XRD) data via the Rietveld method was used in the calcula- tions. This is important, because nanostructures do not possess the same crystal parameters as the bulk and accurate real structural parameters should be used in the calculations. Based on these values, the crystal structures were simulated and the electronic band structures were calculated within the density functional theory (DFT). Results from the density of state (DOS) studies shows that the band-gap narrowing is due to the shifting of the valence and conduction bands. From our theo- retical results, we can conclude that the narrowing of the bandgaps of MgO nanostructures is a consequence of the increase of their lattice parameters. The calculated results exhibit this trend and are in good agreement with the experimental results. Keywords MgO · First principle · Bandgap · DFT · Lattice parameter Introduction It is well known that particle size or, more accurately, crys- tallite size afects the fundamental properties of materials (Heiligtag and Niederberger 2013; Arora et al. 2018). This size dependence can be independently used to manipulate important material properties such as catalytic (Mondal et al. 2016), magnetic (Tlili et al. 2017), electronic (Alves et al. 2018), and intercalation abilities (Lee et al. 2015; Elong and Kamarulzaman 2014). This nanoparticle manipulation has led to various technology applications such as sensors (Lyson-Sypien et al. 2015), solar cells (Masjedi-Arani and Salavati-Niasari 2017), and batteries (Uddin et al. 2017). One of the important characteristics of nanomaterials is the change of bandgap with crystallite size (Singh et al. 2017; Deotale and Nandedkar 2016; Smith and Nie 2009; Zhang et al. 2012). Bandgap is a very important physical criterion of a material and many applications depend on their values. Examples are in semiconductor applications [metal-oxide semiconductor (MOS)] and supercapacitors (Kamarulzaman et al. 2016a, b; Piyadasa et al. 2017). Band-gap changes in metal-oxide nanomaterials have been known and reported previously (Kamarulzaman et al. 2015, 2016; Rusdi et al. 2011). From our previous research, it has been found that, at the nano range, the bandgap of MgO decreases with crystal- lite size (Kamarulzaman et al. 2016). Based on these fnd- ings and to understand the phenomenon better, a theoretical study has been done previously to illustrate the efects of supercell size on band-gap change (Mustafa et al. 2017). However, in this study, we would like to go deeper to inves- tigate the efect of real lattice parameter change of MgO nanostructures on band-gap change from a theoretical point of view. From our literature search, we have not found any studies establishing the connection between cell parameter values and band-gap change. Furthermore, we would like * N. Kamarulzaman norlyk@salam.uitm.edu.my; norly003@yahoo.co.uk 1 Centre for Nanomaterials Research, Institute of Science, Level 3 Block C, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia 2 School of Physics and Materials Studies, Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia