Complete assignment of the vibrational modes of C60 by inelastic neutron scattering spectroscopy and periodic-DFT

Abstract

In this paper we exploit the complementarity of inelastic neutron scattering (INS), infrared and Raman spectroscopies with ab initio calculations to generate an updated assignment of the vibrational modes of C(60). We have carried out periodic-DFT calculations of the high temperature face centred cubic phase modelled as the standard structure and also of the low temperature simple cubic phase, the latter for the first time. Our assignment differs from all previous work, however, it is the only one that is able to successfully reproduce the INS spectrum in terms of both transition energies and intensities. In addition to the INS spectrum we are also able to quantitatively simulate the major features of the infrared and Raman spectra in the high temperature phase and the infrared spectrum in the low temperature phase.

Density functional theory in the solid state

“…Inelastic neutron spectra of the internal modes of C 60 in the Pa3 phase recorded at the ISIS neutron scattering facility on the TOSCA instrument (blue), the MARI instrument (olive green and black) compared with the predicted spectrum from a DFPT calculation (red). Reproduced with permission from PCCP owner societies from Parker et al [67].…”

“…One of the main reasons for the incomplete success of the previous studies was the attempt to compare gas-phase DFT calculations with experiments on solid-state samples. Using the DFPT implementation of AILD in the CASTEP code [66] a series of calculations were performed in close collaboration with an experimental programme of IR, Raman and INS experiments resulting in a definitive account of the entire vibrational spectrum of the low-temperature Pa3 structure and almost all of the observed spectrum of the high-temperature phase [67]. The most powerful of these spectroscopic experiments was INS, because there are no silent modes owing to selection rules unlike IR and Raman scattering.…”

Comment on “Assessment of new DFT methods for predicting vibrational spectra and structure of cisplatin: Which density functional should we choose for studying platinum(II) complexes?” [Spectrochim. Acta A125 (2014) 431–439]

“…This is shown by the excellent agreement between the observed and calculated geometries we obtain [2,3]. Moreover, although it may be true that periodic-DFT methods are not straightforwardly applied to very large systems, they can already handle up to a few hundred atoms already (e.g.…”

“…Moreover, although it may be true that periodic-DFT methods are not straightforwardly applied to very large systems, they can already handle up to a few hundred atoms already (e.g. the low temperature phase of C 60 that contains 240 atoms in the primitive cell [2]), so this is a limitation that will continue to recede as computing power increases.…”

Calculation of the vibrational frequencies of carbon clusters and fullerenes with empirical potentials

“…37,38 There have been many theoretical studies of the vibrational frequencies of C 60 and C 70 using a wide range of different methodologies including force field, 39,40 semi-empirical and DFT. 31,[41][42][43][44][45][46] The work of Hands et al 40 is illustrative of force field based studies, and assessed several existing force fields and developed a new force field wherein the 13 force constants contained within the force field were fitted to the experimental values for the Raman active vibrational modes. This type of model will naturally reproduce the data to which it was fitted but was also able to account for the full spectrum.…”