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Molecular dynamics

Endohedral atoms and cluster in metallofullerenes are usually not tightly fixed. Instead, they exhibit different kinds of motion, from almost free rotation to vibrations with high amplitudes. To study these phenomena, we apply DFT-based Born-Oppenheimer molecular dynamics (BOMD). For paramagnetic states of metallofullerenes, internal dynamics of the clusters can also influence spin density distribution. We have found that even slight changes of the cluster orientation with respect to the carbon cage result in large changes of the spin populations, the effect we have dubbed as 'spin flow'. Following spin density distribution over the molecular dynamics trajectory and applying Fourier transformation to the time dependencies of the atomic spin populations, it is possible to obtain 'spin flow vibrational spectra' which clearly reveal the channels of the spin flow within the molecule.

MD-TiSc2N

BOMD trajectories of TiSc2N@C80 (a, b) and Sc3N@C80– (c, d) at 300 K, 16 picoseconds in microcanonical ensemble. Ti atom is cyan, Sc atoms are in different shades of magenta and violet, nitrogen atom is blue, carbon atoms are gray. In (a) and (c) molecular presentations of trajectories are given (displacement of the carbon atoms are not shown); in (b) and (d) the trajectories are shown in polar coordinates (only angular part) emphasizing rotational component of the displacements. Note that replacement of Sc by Ti substantially hinders rotation of the cluster.

 

MD-Sc2S

 (a) BOMD trajectory of Sc2S@C82 followed for 10 ps in the microcanonical ensemble after equilibration for 0.5 ps at 300 K; Sc atoms are blue and magenta, sulfur atom is yellow, carbon atoms are grey; (b) the same for isostructural Sc2C2@C82; carbon atoms of the carbide unit are light green. For each molecule, two views are shown: one with the C3 axis of the cage perpendicular to the paper, and another one with the axis coplanar to the paper. For Sc2S@C82, BOMD clearly reveals rotation of the Sc2S cluster around the 3-fold axis of the carbon cage.

 

Selected publications:

  1. A. A. Popov, C. Chen, S. Yang, F. Lipps, L. Dunsch. The Spin-Flow Vibrational Spectroscopy of Molecules with Flexible Spin Density: Electrochemistry, ESR, Cluster and Spin Dynamics, and Bonding in TiSc2N@C80. ACS Nano 2010, 4 (8), 4857-4871. DOI: 10.1021/nn101115d
  2. L. Dunsch, S. Yang, L. Zhang, A. Svitova, S. Oswald, A. A. Popov. Metal Sulfide in a C82 Fullerene Cage: A New Form of Endohedral Clusterfullerenes. J. Am. Chem. Soc. 2010, 132, 5413-5421. DOI: 10.1021/ja909580j
  3. A. A. Popov, L. Zhang, L. Dunsch. A pseudoatom in a cage: trimetallofullerene Y3@C80 mimics Y3N@C80 with nitrogen substituted by a pseudoatom. ACS Nano 2010, 4(2), 795-802. DOI: 10.1021/nn901422z