The structures and nonlinear optical responses of superalkali-doped graphyne and boron-doped graphyne: A density functional study

In this work, superalkali M3O (M = Li, Na, K) are adsorbed on graphyne and boron-doped graphyne, where an intramolecular electron donor-acceptor pair is formed. With the increasing atomic number (from the Li3O to the K3O), the adsorption structure on graphyne is obviously different from that on boron-doped graphyne, where the structural integrity of superalkali M3O is still preserved in these molecular systems. The natural bond orbital calculations show that there is electron transfer from the superalkali to the two-dimensional structure, and the net charge transferring values gradually increases with the increasing atomic number. Theoretical calculations show that these systems have large first hyperpolarizabilities. The doping of superalkalis on boron-doped graphyne leads to a larger first hyperpolarizability, which indicates that boron-doped graphyne has advantages in designing nonlinear optical materials than pure graphyne. The first hyperpolarizability increases significantly when heavier superalkali is introduced into the two-dimensional structure, which is found to be 13,854 au for K3O/boron-doped graphyne. It is hoped that this study will inspire more scientists to study the nonlinear optical materials of graphyne.