Nonlinear Optical\nResponse of Tetrel-Modified Tetraphenyl-Adamantane\nClusters

The second harmonic\ngeneration (SHG) properties of adamantane-based\ntetraphenyl clusters are predicted from first principles and analyzed\non the basis of the involved electronic transitions. In particular,\nthe effect of a tetrel substitution in the cluster core on the nonlinear\noptical response is investigated. Electronic transitions spatially\nlocalized at the substituents are found to be responsible for the\noptical nonlinearities. The intensity of the SHG signal grows with\nthe atomic number of the considered tetrel. As the substitution does\nnot distort the cluster core or substantially alter its symmetry,\nthe enhanced SHG intensity is traced to a higher electron density\nat the substituents. The latter results in a larger spatial overlap\nof the states involved in the electronic transitions, which increases\ntheir probability. The presented results provide a theoretical foundation\nfor the design of tailored nonlinear optical sources.