Spectra and excitation properties of (AlP)8: Effect of external electric fields

On the basis of density functional theory (DFT), the geometry and infrared spectrum of the (AlP)8 cluster have been calculated under external electric fields (EEFs). In addition, on the basis of time-dependent DFT, the ultraviolet–visible absorption spectra, oscillator strengths, wavelengths, and hole–electron orbits of the first 20 excited states have been calculated. Under EEFs, the energy of (AlP)8 gradually decreases, the dipole moment increases, and the molecular configuration significantly changes. In the infrared spectrum, the vibration frequency corresponding to the stretching vibration of the Al–P bond decreases, and a red shift occurs. With increasing EEF, the infrared spectrum splits and shows an obvious Stark effect; the ultraviolet absorption intensity is enhanced, and the molecular excitation energy decreases. Additionally, the excitation wavelength increases with increasing EEF. It is conclusively shown that the (AlP)8 cluster is easily excited under an EEF. Separation of the holes and electrons of the (AlP)8 cluster is obvious. Theoretical investigation of the spectra and excitation properties of (AlP)8 is an important step toward a comprehensive understanding of the effects of EEFs on the molecular structure, stability, and dynamics.