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The static (hyper)polarizabilities of the dimer and trimer with diffuse excess electrons, [Li+[calix[4]pyrrole]Li-]n, are firstly investigated by the DFT(B3LYP) method in detail. For the dimer and trimer, a Li atom inside each calix[4]pyrrole unit is ionized to form a diffuse excess electron. The results show that the dimer and trimer containing two and three excess electrons, respectively, have very large first hyperpolarizablities as 2.3 × 104 and 4.0 × 104 au, which are 30 and 40 times larger than that of the corresponding [calix[4]pyrrole]n (n = 2, 3) without Li atom. Also, β values of dimer and trimer are twice and four times as large as that of monomer containing one excess electron. Obviously, not only excess electron but also the number of excess electron plays an important role in increasing the first hyperpolarizability. Moreover, the (hyper)polarizabilities of the [Li+[calix[4]pyrrole]Li-]n polymer are investigated at ab initio level by using the elongation finite-field (elongation FF) method. All the oligomers of the [Li+[calix[4]pyrrole]Li-]n with many excess electrons exhibit very large first hyperpolarizability and large second hyperpolarizability. The present investigation shows that by introducing several and more excess electrons into the nonlinear optical (NLO) materials will be an important strategy for improving their NLO properties, which will be helpful for design of NLO materials. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [ABSTRACT FROM AUTHOR]

The nitrogen edge-doped effect on the structure, dipole moment, and first hyperpolarizability of the supershort single-walled carbon nanotube (5, 0) has been studied systematically. For the nitrogen edge-doped effect on the structure, the mean diameter on the nitrogen-doped side (Du) decreases as the number of doped-nitrogen (n) increases (4.044 (1) > 3.991 (2) > 3.941 (3) > 3.891 (4) > 3.844 Å (5)). Significantly, the nitrogen edge-doped effects on the dipole moment and first hyperpolarizability are revealed for the first time and these new effects are dramatic for the supershort single-walled carbon nanotube (5, 0). Among the β0 values of these seven nitrogen-doped structures, the largest β0 (3155 au) is larger by almost 450 times than the very small β0 (7 au) of undoped structure (D5h). For nitrogen-doped structures, the order of the β0 values is 3155 (1) > 2677 (2A) ≈ 2817 (2B) > 1465 (3A) ≈ 1458 (3B) > 670 (4) > 254 au (5), which shows two interesting relationships between the β0 value and nitrogen-doped number: (1) the smaller the nitrogen-doped number, the larger the β0 value. (2) The structures with the same number of doped-nitrogen have almost the same β0 values (1465 for 3A and 1458 au for 3B). As for the frequency-dependent β (-ω; ω, 0) and β (-2ω; ω, ω), the dependence on the nitrogen-doped number (n) is similar to the case of static β0. For β (-2ω; ω, ω) values at ω = 0.005 au are 3220 (1) > 2720 (2A) ≈ 2862 (2B) > 1480 (3A) ≈ 1477 (3B) > 676 (4) > 256 au (5). In addition, the important monotonic dependences of the β value on the Du and electronic spatial extent ≤R2≥ are also observed. The new knowledge of influence the β value will be beneficial to... [ABSTRACT FROM AUTHOR]

The structures, energetics, spectroscopies, and stabilities of the doublet [Si, C, N, O] radical are explored at the density functional theory and ab initio levels. Sixteen isomers are located, connected by 29 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest lying isomer is a linear SiNCO 1 (0.0 kcal/mol) mainly featuring a cumulene | · Si = N = C = O. The second and third low-lying isomers are bent OSiCN 2 (8.8) and bent OSiNC 3 (11.1), respectively. All the three low-lying isomers 1, 2, 3, and another high-lying species 5 (75.4) with a linear SiCNO structure are shown to have considerable kinetic stability and may be experimentally observable. The predicted results of isomers 1 and 2 are consistent with the previous mass spectrometry experiments. Moreover, the fourth low-lying species SiOCN 4 (23.9) with bent structure is expected to be observable in low-temperature environments. The bonding nature of the five isomers 1, 2, 3, 4, and 5 is analyzed. The calculated results are compared with those of the analogous molecules C2NO and Si2NO. Implications in interstellar space and N,O-doped SiC vaporization processes are also discussed. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 749–761, 2006 [ABSTRACT FROM AUTHOR]