We have performed first-principles calculations of graphene edge stresses, which display two interesting quantum manifestations absent from the classical interpretation: the armchair edge stress oscillates with a nanoribbon width, and the zigzag edge stress is noticeably reduced by spin polarization. Such quantum stress effects in turn manifest in mechanical edge twisting and warping instability, showing features not captured by empirical potentials or continuum theory. Edge adsorption of H and Stone-Wales reconstruction are shown to provide alternative mechanisms in relieving the edge compression and hence to stabilize the planar edge structure.

The self-assembly complexes formed by 2-pyridone derivatives were theoretically studied by the AM1 and DFT methods to determine their binding energies. The UV, IR, and NMR spectra of the complexes were calculated using the INDO/CIS, AM1, and B3LYP/3-21G methods, respectively. It was shown that the complexes could be formed by two monomers via double hydrogen bonding thanks to the negative binding energy. The affinity for binding was increased by substituents in the monomers. But this stimulating effect depended on the simultaneous influence of the electronic and steric effects. The first absorption bands in the UV spectra of the complexes were blue-shifted relative to that of the monomer because of their larger LUMO-HOMO energy gaps. As hydrogen bonds were formed, the N-H stretching vibrations of the monomers were weakened in the IR spectra of the complexes. And the chemical shifts of the C=C and C≡C carbon atoms were shifted downfield in the ¹³C NMR spectra.

Using molecular dynamics (MD) simulations, we have investigated the kinetics of the graphene edge folding process. The lower limit of the energy barrier is found to be ∼380 meV/Å (or about 800 meV per edge atom) and ∼50 meV/Å (or about 120 meV per edge atom) for folding the edges of intrinsic clean single-layer graphene (SLG) and double-layer graphene (DLG), respectively. However, the edge folding barriers can be substantially reduced by imbalanced chemical adsorption, such as of H atoms, on the two sides of graphene along the edges. Our studies indicate that thermal folding is not feasible at room temperature (RT) for clean SLG and DLG edges and is feasible at high temperature only for DLG edges, whereas chemical folding (with adsorbates) of both SLG and DLG edges can be spontaneous at RT. These findings suggest that the folded edge structures of suspended graphene observed in some experiments are possibly due to the presence of adsorbates at the edges.