Density Functional Study of the Influence of Carbon Doping on the Aluminum-27 and Nitrogen-14 Electric Field Gradient Tensors in (10, 0) Single-Walled Aluminum Nitride Nanotube

2008 ◽  
Vol 222 (11) ◽  
pp. 1569-1577
Author(s):  
Ahmad Seif ◽  
Mahmoud Mirzaei
2008 ◽  
Vol 07 (03) ◽  
pp. 447-455 ◽  
Author(s):  
AHMAD SEIF ◽  
ASADOLLAH BOSHRA ◽  
MAHMOUD MIRZAEI ◽  
MEHRAN AGHAIE

Density functional theory (DFT) study is performed to investigate the influence of carbon substituting in a representative model of armchair boron nitride nanotubes (BNNTs). To this aim, the electric field gradient (EFG) tensors at the sites of11B and11N nuclei are calculated in two models of (4,4) single-walled BNNT. Model one (raw) consists of 36 B and 36 N atoms with 12 saturating H atoms of two mouths while 7 B and 7 N atoms are substituted by 14 C atoms like a wire in model two ( C -substituted). The converted EFG tensors to measurable nuclear quadrupole resonance (NQR) parameters, quadrupole coupling constant (CQ) and asymmetry parameter (ηQ), reveal that the CQvalues in the length of raw BNNT are divided into some layers with equal magnitude and among them the mouth layers have the largest CQmagnitudes. In the C -substituted model, in addition to the mouth layers, the CQof those B and N nuclei directly bonded to C atoms are increased to the magnitudes as large as those mouth nuclei meaning that the active sites are increased in the C -substituted BNNT model. It is worth noting that the NQR parameters of other nuclei rather than those directly bonded to C and also those in the first neighborhood of C atoms are almost in equal values in the two models. Comparing the results with a recent study on zigzag BNNT (Mirzaei M et al., Z. Naturforsch A62:56, 2007) reveals that armchair and zigzag BNNTs show almost similar electronic properties. However, there is a significant difference in the electronic properties of those B and N atoms located at the mouth of the two BNNTs whose mouths are similar in armchair, whereas there are two different mouths ( B -mouth and N -mouth) in zigzag BNNT.


2006 ◽  
Vol 61 (7-8) ◽  
pp. 383-388 ◽  
Author(s):  
Tayyebeh Partovi ◽  
Mahmoud Mirzaei ◽  
Nasser L. Hadipour

A density functional study was carried out to investigate the C-H···O hydrogen bonding effects on the 17O electric field gradient and chemical shielding tensors in crystalline 1-methyluracil. Since the structural coordinates were obtained from a neutron diffraction study, no geometry optimization was needed in performing the calculations. It is demonstrated that C-H···O hydrogen bonding has different influences on O2 and O4 EFG and CS tensors. In the tetramer model of 1-methyluracil, which is much closer to the real crystalline phase, the influence of C-H···O on the O4 EFG and CS tensors is significant, whereas this influence is negligible for O2.


2007 ◽  
Vol 62 (12) ◽  
pp. 711-715 ◽  
Author(s):  
Ahmad Seif ◽  
Mahmoud Mirzaei ◽  
Mehran Aghaie ◽  
Asadollah Boshra

Density functional theory (DFT) calculations were performed to calculate the electric field gradient (EFG) tensors at the sites of aliminium (27Al) and nitrogen (14N) nuclei in an 1 nm of length (6,0) single-walled aliminium nitride nanotube (AlNNT) in three forms of the tubes, i. e. hydrogencapped, aliminium-terminated and nitrogen-terminated as representatives of zigzag AlNNTs. At first, each form was optimized at the level of the Becke3,Lee-Yang-Parr (B3LYP) method, 6-311G∗∗ basis set. After, the EFG tensors were calculated at the level of the B3LYP method, 6-311++G∗∗ and individual gauge for localized orbitals (IGLO-II and IGLO-III) types of basis sets in each of the three optimized forms and were converted to experimentally measurable nuclear quadrupole resonance (NQR) parameters, i. e. quadrupole coupling constant (qcc) and asymmetry parameter (ηQ). The evaluated NQR parameters revealed that the considered model of AlNNT can be divided into four equivalent layers with similar electrostatic properties.With the exception of Al-1, all of the three other Al layers have almost the same properties, however, N layers show significant differences in the magnitudes of the NQR parameters in the length of the nanotube. Furthermore, the evaluated NQR parameters of Al-1 in the Al-terminated form and N-1 in the N-terminated form revealed the different roles of Al (base agent) and of N (acid agent) in AlNNT. All the calculations were carried out using the GAUSSIAN 98 package program.


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