  The ground state of odd-N polyynic oligomers C_{N}H_{2} features
kink-solitons in carbon-carbon bond-length alternation (BLA) patterns. We
perform a systematic first-principles computational study of neutral and
singly-charged kinks in long oligomers addressing relationships between BLA
patterns, electron energy gaps, and accompanying distributions of spin and
charge densities, both in vacuum and in the screening solvent environment. A
quantitative comparison is made of the results derived with four different ab
initio methods: from pure DFT to pure Hartree-Fock (HF) and including two
popular hybrid density functionals, B3LYP and BHandHLYP. A clear correlation is
demonstrated between the derived spatial extent of kinks and the amount of HF
exchange used in the functionals. For charged kinks, we find a substantial
difference in the behavior of charge and spin densities.
