Journal Article strain energy phonon frequencies HSE0 exchange-correlation functional Research Support, Non-U.S. Gov't carbon nanotubes high pressure layered compound nanolayers phonon dispersion thermodynamic properties of nanotubes zone folding Bilbao Crystallographic Server DFT calculations FePS3 FePSe3 Helmholtz energy LSITESYM Line and Rod groups MoS2 monolayer MoS2 nanotubes PBE0 calculations V2O5 nanotubes argentophillic interactions axial point group irreducible representations density functional calculations double-walled nanotubes electron density topological analysis entropy first principles calculations