  A continuous model of double-walled carbon nanotube (DWCNT) low-frequency
dynamics was constructed. In the frame of the approach proposed formation of a
DWCNT low-frequency phonon spectrum from the ones of corresponding
single-walled carbon nanotubes (SWCNTs) was considered. Environmental influence
on the individual DWCNT phonon spectrum was studied. A combined method of van
der Waals interlayer coupling coefficients evaluation was proposed, and it is
based on Raman spectroscopy data and known values of graphite elastic moduli.
Also DWCNT low-temperature specific heat was calculated. In the model
applicability region (at temperatures lower than 35 K) DWCNT specific heat
turned out to be significantly lower than the specific heat sum of
corresponding individual single-walled SWCNTs. This effect is caused mainly by
the interlayer coupling instead of DWCNT interaction with environment.
