Vibrational properties of single-molecule magnet Fe4

A single-molecule magnet (SMM) Fe$_4$ consists of four Fe ions interacting through O anions via antiferromagnetic superexchange coupling, with the total ground-state spin of $S=5$. The SMM Fe$_4$ has a magnetic anisotropy energy of $16$ K, and its ground-state spin multiplet is well separated from the first excited spin multiplet. A recent experimental effort demonstrated that SMMs Fe$_4$ can be deposited on various substrates with magnetic cores intact and that individual Fe$_4$ molecules can be bridged between electrodes. SMMs Fe$_4$ deposited on substrates or in contact with electrodes revealed interesting magnetic and transport properties. Electronic and spin degrees of freedom of SMM Fe$_4$ may be coupled to vibrational degrees of freedom. Such coupling can affect various properties of SMM Fe$_4$. Here we present our calculation of vibrational spectra (Raman and infrared) of SMM Fe$_4$ using density-functional theory (DFT) within simple harmonic oscillator approximation. We identify normal modes and compare our calculated result with available experimental data.