Lone pair cations have an s2 p0 valence electron configuration as found in Sn(II), Pb(II) and Bi(III). Non-centrosymmetric external electric fields around such a cation stabilise the two valence electrons as a localised off-centre lone pair lobe formed by hybridisation of s and p type valence orbitals, that cause structural distortions in a wide class of material. Due to the exciting properties derived from the polarisation of the lone pair and the interest in potential applications, materials including lone pair cations have been attracting huge attention in the materials community.
As an approach to study materials including lone pair cations, computational methods have been widely employed, and electronic structure techniques are used most frequently. There is a deficit of physiochemically accurate and computationally affordable models for these materials within classical atomistic approaches.
To address this issue, we have developed an efficient model for simulating the lone pair cations, employing a simple concept from quantum mechanics of a single-electron molecular orbital to treat the electron lone pair. Throughout this thesis, we developed theoretical basis of the lone pair model, including mathematical and technical details used as recipes for the model implementation in our in-house software package, SLAM, which is freely available to download from the GitHub. For validation of our approach, we investigated the model properties, including high order electric multipoles and their polarisabilities, which were compared to their counterparts obtained using an electronic structure method, and our approach has turned out to be effective. Finally, the new lone pair model was employed to simulate nanoclusters of lead monoxide and difluoride as its application, and it was evidenced by the results that the lone pair model is efficient and accurate in predicting and reproducing the nanocluster atomic configurations, obtained using density functional theory.