Calculation of the Stability and the Polarizability of Isolated Fullerene Molecules as a Function of Charge State
- PDF / 394,334 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 32 Downloads / 164 Views
CALCULATION OF THE STABILITY AND THE POLARIZABILITY OF ISOLATED FULLERENE MOLECULES AS A FUNCTION OF CHARGE STATE ANDREW A. QUONG° AND MARK R. PEDERSON Complex Systems Theory Branch, Washington, DC 20375-5000 *NRC-NRL Research Associate
Code 4690, Naval
Research Laboratory,
ABSTRACT We present first-principles local density functional calculations of the electronic structure and energetics of neutral and negatively charged fullerene molecules. We find that the negatively charged -1 state is stable relative to the neutral molecule and that the -2 state is stable relative to the neutral molecule but not to the -1 state of the molecule. We have also performed calculations of the electronic polarizabilities for different charged states and developed a simple model to estimate the dielectric constant of fullerene based crystals. INTRODUCTION To aid in the understanding of how fullerene molecules interact with each other and behave in different environments, we have performed first principles calculations of different physical properties of isolated fullerene molecules. We first determined the relative stability of the different charge states of the fullerene molecule by performing total energy calculations within the framework of density functional theory, using the recently developed all-electron full-potential gaussian-orbital cluster codes [1]. For the neutral molecule we find bond lengths of 2.642 and 2.741 bohr for the hexagonal and pentagonal bonds, which are in good agreement with experiment. We have also employed the generalized gradient approximation to calculate the electron affinities. Density functional theory also allows us to calculate the energy of the molecule in a static electric field which allows us to determine the polarizability of the fullerene molecule from first principles. STABILITY OF CHARGE STATES To understand the energetics of the different charge states of the negatively charged fullerene molecule, we have performed several levels of SCF calculations. We first performed spin-unpolarized calculations without geometric relaxation for the different charge states by changing the occupation of the Tlu molecular orbital. By performing calculations for Q = 0, Q = 3, and Q = 6, we determined that the energy as a function of charge state can written as E(Bb) = -3.21 + 1.52(Q-1.46)2 eV. Using this relation, we find the first electron affinity to be -2.89 eV and the second electron affinity to be 0.11 eV, i.e. the negative charged -1 state is stable relative to the neutral molecule and the -2 state is slightly unstable with respect to the -1 state, but stable relative to the neutral fullerene molecule. We find fair agreement with the experimental value of the first electron affinity of -2.74 eV [2]. Because the second electron affinity is close to zero, we performed more accurate calculations that included geometrical relaxation and spin-polarization. In Mat. Res. Soc. Symp. Proc. Vol. 270. @1992 Materials Research Society
210
relaxing the atomic coordinates for the charged molecules, we have ma
Data Loading...
