[en] In this paper we study low-lying states of even-even nuclei in the sd and pf shells in the framework of the shell model with the phenomenological pairing plus quadrupole-quadrupole (P + Q) interaction. By adopting the single-particle energy and the monopole interaction from the USDB and GXPF1 interactions, the low-lying spectra of spherical nuclei and deformed nuclei are successfully reproduced by a unified set of parameters. We obtain a reasonably good result for binding energies by removing the monopole component from the pairing interactions. The isoscalar pairing interaction does not play an important role in the states. The monopole interaction provides contributions to the empirical proton-neutron interaction, the symmetry energy, and the Wigner energy. (authors)

[en] Background: Nucleon-pair correlations play an important role in low-lying states of atomic nuclei. Purpose: The aim is to study empirical proton-neutron interactions and investigate the contribution from spin-aligned proton-neutron pairs (with spin 9 and isospin 0) in low-lying states of ⁹⁶Cd and ⁹²Pd. Methods: The empirical proton-neutron interaction is obtained by using nuclear binding energies of a few neighboring nuclei and the nuclear shell model. The contribution from spin-aligned proton-neutron pairs in the shell model wave functions is evaluated by using the nucleon-pair approximation with isospin symmetry. Results: The empirical proton-neutron interaction is reasonably consistent with isoscalar interactions calculated by using the shell model. There exists an additional binding energy in both even-even and odd-odd nuclei originated from proton-neutron interactions. Spin-aligned isoscalar pairs play an important role in the 0₁⁺, 2₁⁺, 4₁⁺, 6₁⁺, 12₁⁺, 14₁⁺and 16₁⁺ states of ⁹⁶Cd and the 0₁⁺, 2₁⁺ states of ⁹²Pd. For the 0₁⁺ and 2₁⁺ states, the conventional isovector SD pairs are more relevant. Conclusion: Both isoscalar and isovector nucleon pairs play an important role in low-lying states of N = Z nuclei. This is a consequence of nonorthogonality feature of nucleon-pair basis. (authors)

[en] The encapsulation of C₆₀ into single-wall carbon nanotubes is systematically studied by tight-binding molecular dynamics method with an appropriate long-range Lennard-Jones potentials. For a (16,0) nanotube, it is impossible to encapsulate C₆₀ into the tube because of a much larger energy barrier with the relaxation of the open end.