Effect of alkaline earth metal atom on the large static first hyperpolarizabilities of alkaline earth-based alkalides Be(NH3)nM (M = Be and Ca) in comparison with alkalides Li(NH3)nNa (n = 1–3)

Can alkaline-earth-doped compounds with alkalide features be candidates of high-performance nonlinear optical (NLO) materials? In this paper, by comparing with sodides Li(NH3)nNa (n = 1–3) (Jing et al., 2006), the structures and the NLO properties of Be(NH3)nM (M = Be and Ca) have been studied. Similar to the alkalide characteristics of Li+(NH3)nNa−, both the absolute value of the negative charge of M and static first hyperpolarizability (β0) of Be(NH3)nM increase with increasing the NH3 coordination number, which suggests these (Be(NH3)n)+M− not only present unusual alkaline earth-based alkalide’s features but also exhibit dramatically large static β0 up to 1.26 × 105 au (Be(NH3)3Be). Except the Be(NH3)Be, the β0 of each Be(NH3)nM with alkaline earth-based alkalide feature is much larger than that of the corresponding Li(NH3)nNa with alkalide feature. Significantly, from Li(NH3)2Na to Be(NH3)2Ca and from the Li(NH3)3Na to the Be(NH3)3M (M = Be or Ca), the every rise of the β0 value constitutes an order of magnitude improvement. These exhibits a more excellent effect on the β0 value for alkaline earth metal atom doping than for alkali metal atom doping effect, which suggests that, besides the alkaline metal atom doping, the alkaline earth metal atom doping is also an important and well-performance method to enhance the NLO responses.