Theoretical study of the single walled carbon nanotube (4, 0) properties under external electric fields
D. Farmanzadeh and A. Amirazami
Faculty of chemistry, University of Mazandaran, Babolsar, P. O. Box: 453, I. R. Iran.
[email protected] and [email protected]
Introduction
The physics of carbon nanotubes has rapidly evolved into a research field since their discovery by Iijima in multiwall form in 1991 [1] and as single-walled tubes two years later. In recent years, the single-walled carbon nanotubes (SWCNT) attracted considerable attention due to their importance as building block in nanotechnology.
The strength and flexibility of carbon nanotubes (CNs) makes them of potential use in controlling other nanoscale structures, which suggests they will have an important role in nanotechnology engineering. CNs have already been used as composite fibers in polymers to improve the mechanical, thermal and electrical properties of the bulk product.
The action of external electric field alters the electronic character of the Carbon nanotubes. The understanding of these changes and its manipulation are important for using CNs in electrical circuits as ideal device [2-4].
In this work, we calculate and analyze the structural and electrical properties of SWCNT (4, 0) under the presence of an applied external electric field.
Computational procedures
Calculation of the structural and electronic properties of the zigzag (4, 0) SWCNT over the ranges of the 0 - 2×10-2 a.u. (1 a.u. = 514.224 V/nm) field strength are performed using Gaussian 2003 program, at DFT-B3LYP level of theory with the 6-31G* basis set.
We chose the standard direction of an electric dipole field along + X axis, Figure 1.
Results and Discussion
The field effects results show that the variation of structural parameters are not considerable over the entire ranges of the applied field strength (0 - 2×10-2 a.u. ; maximum changes: bond lengths <2.4%, bond angles <8.7%, dihedral angles <4.1%).
Electronic spatial extent (ESE) value shows a small increasing trend in the presence of electric field (<1%).
Electric dipoles moment in Debye as function of the applied electric field strength are demonstrated in Figure 2. This Figure shows that both |µX| and µ varies considerably from 0.004 and 0.008 Debye at zero field strength to 20.323 and 21.573 at 2×10-2 a.u.
respectively. This result shows that the induced polarization of nanotube increases with increasing the electric field strength and nanotube oriented with its negative ends toward the positive pole.
Trends of the Occupied (O) and virtual (V) molecular orbital energies including ELUMO
and EHOMO calculated for the nanotube at different electric field strength are plotted in Figure 3. This Figure show that values of frontier orbital energies increases gradually over the ranges of the applied field strength, however the HLG values (HLG = ELUMO- EHOMO) are slightly decreased.
The natural bond orbital (NBO) electric charges on atoms of the SWCNT (4, 0) shows that presence of the external electric field changes the atomic charges and the magnitude of these changes for each atom increases with increasing strength of the applied electric field.
References
1. S. Iijima, Nature 354, 56 (1991).
2. Yu. Min- Feng, Science 287, 637 (2000).
1. S. Reich, et al., Carbon Nanotubes ; Wiley, Weinheim, Germany, (2004).
2. S.V. Rotkin, S. Subramoey, Applied Physics of Carbon Nanotubes ; Springer, Berlin, Germany (2005).
Figure 1. The SWCNT (4, 0) structure, which its response to the external electrical field is studied in this work at DFT-B3LYP/6-31G* level of theory.
Orbital Energy (e v)
30 total
x y
20 z 0
10 -1
0
-10
-20
-30
0 50 100 150 200 250
Field strength (10-4 a.u.)
-2
-3
-4
-5
-6
0 50 100 150 200 250
Field Strength (10-4 a.u.)
V-2
V-4 V-3 V-2 V-1 O-1 O-2 O-3 O-4
O-5
Dipole Moment (Debye)
1
