Correlation between thermal conductivity and bond length alternation in carbon nanotubes: A combined reverse nonequilibrium molecular dynamics—Crystal orbital analysis

Abstract

The thermal conductivity (λ) of carbon nanotubes (CNTs) with chirality indices (5,0), (10,0), (5,5), and (10,10) has been studied by reverse nonequilibrium molecular dynamics (RNEMD) simulations as a function of different bond length alternation patterns (Δr(i) ). The Δr(i) dependence of the bond force constant (k(rx) ) in the molecular dynamics force field has been modeled with the help of an electronic band structure approach. These calculations show that the Δr(i) dependence of k(rx) in tubes with not too small a diameter can be mapped by a simple linear bond length-bond order correlation. A bond length alternation with an overall reduction in the length of the nanotube causes an enhancement of λ, whereas an alternation scheme leading to an elongation of the tube is coupled to a decrease of the thermal conductivity. This effect is more pronounced in carbon nanotubes with larger diameters. The formation of a polyene-like structure in the direction of the longitudinal axis has a negligible influence on λ. A comparative analysis of the RNEMD and crystal orbital results indicates that Δr(i) -dependent modifications of λ and the electrical conductivity are uncorrelated. This behavior is in-line with a heat transfer that is not carried by electrons. Modifications of λ as a function of the bond alternation in the (10,10) nanotube are explained with the help of power spectra, which provide access to the density of vibrational states. We have suggested longitudinal low-energy modes in the spectra that might be responsible for the Δr(i) dependence of λ.

Influence of longitudinal isotope substitution on the thermal conductivity of carbon nanotubes: Results of nonequilibrium molecular dynamics and local density functional calculations

“…Limitations of the employed force-field in the reproduction of high energy vibrations have already been seen in a combined MD-band structure approach study of CNTs. 47 It can also be said that different classical force-fields may yield different phonon properties with slight differences in the distribution of frequencies. However, an important feature in connection with thermal conductivity studies is their ability to reproduce correctly the formation of acoustic modes with high group velocities.…”

Transversal thermal transport in single-walled carbon nanotube bundles: Influence of axial stretching and intertube bonding

“…[10][11][12][13][14] The energy transport in single-walled and multi-walled nanotubes (SWNTs, MWNTs) has been investigated extensively both by theoretical models and experimental techniques. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] The highest λ values of roughly 3500 W/mK have been measured in the axial direction of isolated tubes. 10 They are a result of an efficient phonon support via longitudinal acoustic modes of large mean free paths.…”

“…10 They are a result of an efficient phonon support via longitudinal acoustic modes of large mean free paths. 15,16 Thermal conductivity calculations of isolated CNTs were performed as a function of the temperature, 13,14,[16][17][18] chain length, [18][19][20] atomic defects, 12,21,22 impurities, 18,23 tube diameter, 14,17 chirality of the tubes, 17,18 bond length alternation, 24 and a forced axial strain. [25][26][27] For applications, however, the thermal conductivity of (ordered) CNT ensembles (e.g., bundles, films ) is more important than λ numbers measured in isolated CNTs.…”

Heat transport enhanced by optical phonons in one-dimensional anharmonic lattices with alternating bonds

“…In particular, it can model the carbon nanotubes with bond length alternation, since the bond force constant depends on the length. Recently, the thermal conductivity in nanotubes with bond length alternation has been investigated by molecular dynamics and crystal orbital analysis [26]. It has been found that the bond alternation can strongly modify the thermal conductivity in the armchair nanotubes.…”