Zurek Eva, Pickard Chris J, Walczak Brian, Autschbach Jochen
Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart, Germany.
J Phys Chem A. 2006 Nov 2;110(43):11995-2004. doi: 10.1021/jp064540f.
NMR chemical shifts were calculated for semiconducting (n,0) single-walled carbon nanotubes (SWNTs) with n ranging from 7 to 17. Infinite isolated SWNTs were calculated using a gauge-including projector-augmented plane-wave (GIPAW) approach with periodic boundary conditions and density functional theory (DFT). In order to minimize intertube interactions in the GIPAW computations, an intertube distance of 8 A was chosen. For the infinite tubes, we found a chemical shift range of over 20 ppm for the systems considered here. The SWNT family with lambda = mod(n, 3) = 0 has much smaller chemical shifts compared to the other two families with lambda = 1 and lambda = 2. For all three families, the chemical shifts decrease roughly inversely proportional to the tube's diameter. The results were compared to calculations of finite capped SWNT fragments using a gauge-including atomic orbital (GIAO) basis. Direct comparison of the two types of calculations could be made if benzene was used as the internal (computational) reference. The NMR chemical shifts of finite SWNTs were found to converge very slowly, if at all, to the infinite limit, indicating that capping has a strong effect (at least for the (9,0) tubes) on the calculated properties. Our results suggest that (13)C NMR has the potential for becoming a useful tool in characterizing SWNT samples.
计算了n值范围为7至17的半导体(n,0)单壁碳纳米管(SWNTs)的核磁共振化学位移。使用包含规范投影增强平面波(GIPAW)方法并结合周期性边界条件和密度泛函理论(DFT)计算了无限长孤立的SWNTs。为了在GIPAW计算中最小化管间相互作用，选择了8埃的管间距离。对于无限长的管子，我们发现这里考虑的系统的化学位移范围超过20 ppm。与λ = mod(n, 3) = 1和λ = 2的其他两个家族相比，λ = mod(n, 3) = 0的SWNT家族的化学位移要小得多。对于所有三个家族，化学位移大致与管的直径成反比减小。将结果与使用包含规范的原子轨道(GIAO)基组对有限封端SWNT片段的计算进行了比较。如果使用苯作为内部(计算)参考，则可以对这两种类型的计算进行直接比较。发现有限SWNTs的核磁共振化学位移向无限极限收敛得非常缓慢，甚至根本不收敛，这表明封端对计算性质有很强的影响(至少对于(9,0)管)。我们的结果表明，(13)C核磁共振有潜力成为表征SWNT样品的有用工具。
