Investigating anharmonicity using molecular dynamics calculations: the TM hydride series (PH3)3MH4, (M = Os, Ru and Fe)

Abstract

We present an ab initio molecular dynamics study of the iron triad complex (PH₃)₃MH₄, (M = Os, Ru and Fe). We calculate numerical atomic probability density functions (PDFs), which offer direct visualisation of the degree of anharmonicity present in these complexes. Fitting our calculated PDFs to a parabolic transformation of the standard crystallographic ellipsoidal PDF allowed the bond correction for librational motion observed in the M–H distances to be obtained. For the Ru and Fe complexes we also attempt to quantify the bond distance correction needed to describe the η²-bound H₂ ligand anharmonically. From our simulations we also obtain anharmonic vibrational spectra, which we compare to experimental data. Finally, we also comment on a spontaneous H₂/(H)₂ ligand flipping process observed for the Fe complex.