Showing papers by "Susumu Saito published in 1999"
TL;DR: In this paper, the total energy calculations in the density-functional theory were used to explore new polymerized fullite phases by using the total-energy calculations in density functional theory starting from two dimensionally polymerized tetragonal phase.
Abstract: We explore new polymerized ${\mathrm{C}}_{60}$ fullerite phases by using the total-energy calculations in the density-functional theory Starting from the two dimensionally polymerized tetragonal phase, we find a new stable three dimensionally polymerized structure to be synthesized under uniaxial pressure of about 20 GPa In sharp contrast to other polymerized ${\mathrm{C}}_{60}$ phases and to solid ${\mathrm{C}}_{60}$, the new polymer possesses metallic electronic structure with a relatively large Fermi-level density of states Its conduction-electron distribution and the energetics are studied in detail
98 citations
TL;DR: In this article, the electronic structure and energetic stabilities of two-dimensional polymers, in both tetragonal and rhombohedral phases, studied by using the local density approximation in the framework of the density functional theory.
Abstract: We report on the electronic structure and energetic stabilities of two-dimensional ${\mathrm{C}}_{60}$ polymers, in both tetragonal and rhombohedral phases, studied by using the local-density approximation in the framework of the density-functional theory. Owing to hybrid networks of ${\mathrm{sp}}^{2}$-like (threefold coordinated) and ${\mathrm{sp}}^{3}$-like (fourfold coordinated) carbon atoms, the electronic structure of these phases is considerably different from that of face-centered-cubic (fcc) ${\mathrm{C}}_{60}.$ Both systems are found to be elemental semiconductors having small indirect gaps. Furthermore, since the interlayer distance between adjacent polymerized planes for both phases is small, these systems are found to have three-dimensional electronic structures. From structural optimizations under the experimental lattice parameters, we reveal energetic high stabilities of these phases. In particular, the tetragonal phase is found to be considerably more stable in energy than the fcc phase. Its high stability is caused by the formation of intercluster bonds whose energy gain is larger than the energy loss due to the distortion of the carbon networks of ${\mathrm{C}}_{60}$ units upon polymerization.
86 citations
TL;DR: In this paper, the electronic structure of the superconducting fullerides was studied using the local density approximation in the density functional theory, and the conduction-band profiles were quantitatively very similar to each other.
Abstract: We have studied the electronic structure of the superconducting fullerides ${\mathrm{K}}_{3}{\mathrm{Ba}}_{3}{\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}{\mathrm{Ba}}_{3}{\mathrm{C}}_{60}$ using the local-density approximation in the density functional theory. Their conduction-band profiles are found to be quantitatively very similar to each other although the lattice constant of ${\mathrm{K}}_{3}{\mathrm{Ba}}_{3}{\mathrm{C}}_{60}$ is definitely smaller than that of ${\mathrm{Rb}}_{3}{\mathrm{Ba}}_{3}{\mathrm{C}}_{60}.$ The density of states at Fermi level of ${\mathrm{K}}_{3}{\mathrm{Ba}}_{3}{\mathrm{C}}_{60}$ is slightly larger than that of ${\mathrm{Rb}}_{3}{\mathrm{Ba}}_{3}{\mathrm{C}}_{60}.$ In addition, ${\mathrm{C}}_{60}$ states are found to be hybridized not only with Ba states but also with K (Rb) states. These results are in sharp contrast to ${A}_{3}{\mathrm{C}}_{60}$ superconductors $(A=\mathrm{K}$ and Rb). The hybridization is expected to play an important role in their superconducting properties since carriers are found to be not only on ${\mathrm{C}}_{60}$ but also around K (Rb) sites as well as Ba sites.
13 citations
TL;DR: In this paper, the electronic structure of potassium-doped crystalline lattice of so-called (10.10) carbon nanotubes in the framework of the density-finctional theory was studied.
Abstract: We study the electronic structure of potassium-doped crystalline lattice of so-called (10.10) carbon nanotubes in the framework of the density-finctional theory. Tie stoichiometrv of the material studied is K2C80 which was originally proposed in designing the superconducting doped nanotube material based on tile size of dopants and the charge transfer being favorable for superconductivity. Electronic band dispersions obtained are actually found to be very similar to those of the pristine (10,10) nanotube lattice with the upward shift of the Fermi energy by 1 eV above the second conduction-band miinimum. Tie system therefore possesses higher Fermi-level density of states than the pristine material with rather sinmple charge transfer from K to C sites, and is confirned to be a good candidate for a naxiotube superconductor.
1 citations
TL;DR: In this article, the optical absorption spectra of Na clusters using the time-dependent density-functional theory with gradient correction was studied and a jellium-sphere background model, which is free from basis-set incompleteness error and is suitable for the comparison of various theoretical methods, was adopted.
Abstract: We study tile optical absorption spectra of Na clusters using the time-dependent density-functional theory with gradient correction. A jellium-sphere background model, which is free from basis-set incompleteness error and is suitable for the comparison of various theoretical methods, is adopted. For energies of surface-plasinon excitations governing profiles of photoabsorption spectra with huge oscillator strengths., the gradient correction by van Leeiiwen and Baerends with correct asymptotic behavior of the effective potential is found to show considerable improvement over the time-dependent local-density approximation.