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Chattopadhyaya M Alam MM Chakrabarti S 《Physical chemistry chemical physics : PCCP》2012,14(26):9439-9443
Herein, we predict that graphene nanoribbons will be nonplanar under the influence of a critical perpendicular field. Our investigation demonstrates that the perpendicular field induces mixing of σ and π orbitals in graphene nanoribbons through the second order Stark effect which eventually modulates the electron-nuclear interaction strongly in favor of a bent structure. 相似文献
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Ray M Nakao Y Sato H Sakaba H Sakaki S 《Journal of the American Chemical Society》2006,128(36):11927-11939
The geometry and bonding nature of Cp(CO)(2)W(CCH)(SiH(2)) (1) and the reaction leading to the formation of 1 from Cp(CO)(2)W(SiH(2)C triple bond CH)(9) were theoretically investigated with DFT, MP2 to MP4(SDTQ), and CCSD(T) methods, where 9 and 1 were adopted as models of the interesting new complexes reported recently, Cp*(CO)(2)W(Si(Ph)(2)C triple bond C(t)Bu) and Cp*(CO)(2)W(C triple bond C(t)Bu)(SiPh(2)), respectively. Our computational results clearly indicate that 1 involves neither a pure silacyclopropenyl group nor pure silylene and acetylide groups and that the silylene group strongly interacts with both the W center and the acetylide group. Frontier orbitals of 1 resemble those observed in the formation of silacyclopropene from silylene and acetylene. The frontier orbitals, as well as the geometry, indicate that the (CCH)(SiH(2)) moiety of 1 can be understood in terms of an interesting intermediate species trapped by the W center in that formation reaction. Complex 1 is easily formed from 9 through Si-C sigma-bond activation with moderate activation barriers of 15.3, 18.8, and 15.8 kcal/mol, which are the DFT-, MP4(SDTQ)-, and CCSD(T)-calculated values, respectively. This reaction takes place without a change of the oxidation state of the W center. Intermediate 9 is easily formed from Cp(CO)(2)W(Me)(H(3)SiC triple bond CH) via Si-H oxidative addition, followed by C-H reductive elimination. The bonding nature of 9 is also very interesting; the nonbonding pi-orbital of the H(2)SiCCH moiety is essentially the same as that of the propargyl group, but the pi-conjugation between Si and C atoms is very weak in the pi-orbital, unlike that in the propargyl group. 相似文献
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Alam MM Chattopadhyaya M Chakrabarti S 《Physical chemistry chemical physics : PCCP》2012,14(3):1156-1165
For the first time, we report the effect of interference between different optical channels on the two-photon absorption (TPA) process in three dimensions. We have employed response theory as well as a sum-over-states (SOS) approach involving few intermediate states to calculate the TPA parameters like transition probabilities (δ(TP)) and TPA tensor elements. In order to use the limited SOS approach, we have derived a new formula for a generalized few-state-model (GFSM) in three dimensions. Due to the presence of additional terms related to the angle between different transition moment vectors, the channel interference associated with the TPA process in 3D is significantly different and much more complicated than that in 1D and 2D cases. The entire study has been carried out on the two simplest Reichardt's dyes, namely 2- and 4-(pyridinium-1-yl)-phenolate (ortho- and para-betain) in gas phase, THF, CH(3)CN and water solvents. We have meticulously inspected the effect of the additional angle related terms on the overall TPA transition probabilities of the two 3D isomeric molecules studied and found that the interfering terms involved in the δ(TP) expression contribute both constructively and destructively as well to the overall δ(TP) value. Moreover, the interfering term has a more conspicuous role in determining the net δ(TP) associated with charge transfer transition in comparison to that of π-π* transition of the studied systems. Interestingly, our model calculations suggest that, for o- and p-betain, the quenching of destructive interference associated with a particular two-photon process can be done with high polarity solvents while the enhancement of constructive interference will be achieved in solvents having relatively small polarity. All the one- and two-photon parameters are evaluated using a range separated CAMB3LYP functional. 相似文献
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A. Maitra Mausumi Kundu 《International Journal of Infrared and Millimeter Waves》2003,24(11):1841-1851
The propagation of wideband signals through the atmosphere has been studied at millimeter wavelengths at which the atmosphere exhibits significant dispersion as well as absorption. The wideband signals having a Gaussian spectrum are considered to be propagating at carrier frequencies in the range 10-200 GHz over line-of-sight paths under varying propagation conditions effected by the clear air and raining atmosphere. The propagation effects on the wideband signal are assessed in terms of the percentage change in the width and the group delay suffered by the pulsed envelope, also having a Gaussian shape, and the shift in the mode frequency of the signal. The results of numerical calculations, based on a closed solution of Fourier integral, show that the propagated wideband signal can be significantly affected by the atmosphere depending on rain rate, carrier frequency, path length and signal bandwidth. 相似文献
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Hazarika Jnyandeep Ganguly Mausumi Borgohain Gargi Baruah Indrani Sarma Shruti Bhuyan Pranjal Mahanta Rita 《Structural chemistry》2020,31(5):2011-2021
Structural Chemistry - Chlorpyrifos is an extensively used organophosphate pesticide showing broad-spectrum effectiveness on various target pests. Long-term sublethal exposure to this pesticide is... 相似文献
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In (2,n) visual cryptographic schemes, a secret image(text or picture) is encrypted into n shares, which are distributed among n participants. The image cannot be decoded from any single share but any two participants can together decode it visually,
without using any complex decoding mechanism. In this paper, we introduce three meaningful optimality criteria for evaluating
different schemes and show that some classes of combinatorial designs, such as BIB designs, PBIB designs and regular graph
designs, can yield a large number of black and white (2,n) schemes that are optimal with respect to all these criteria. For a practically useful range of n, we also obtain optimal schemes with the smallest possible pixel expansion. 相似文献
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Key predistribution schemes for distributed sensor networks have received significant attention in the recent literature. In this paper we propose a new construction method for these schemes based on combinations of duals of standard block designs. Our method is a broad spectrum one which works for any intersection threshold. By varying the initial designs, we can generate various schemes and this makes the method quite flexible. We also obtain explicit algebraic expressions for the metrics for local connectivity and resiliency. These schemes are quite efficient with regard to connectivity and resiliency and at the same time they allow a straightforward shared-key discovery. 相似文献
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Mausumi Chattopadhyaya Sabyasachi Sen Md.Mehboob Alam Swapan Chakrabarti 《Journal of Physics and Chemistry of Solids》2014
The present study deals with the relative performance of the various density functional approaches in evaluating the band gap of polymer materials. Several density functional approximations that includes pure generalized gradient approximated (GGA) functional, meta-GGA, hybrid and range separated hybrid functionals have been used to evaluate the electrical band gap or transport gap of the studied polymers and compared with that obtained using Hubbard U corrected GGA functional (GGA+U). It has been observed that the experimental band gap of the polymers studied is satisfactorily reproducible when GGA+U approach is adopted. The band gap analyses further suggest that range separated hybrid functional, CAM-B3LYP, largely overestimates the band gap of all the polymers studied while the performance of hybrid B3LYP functional and other range separated hybrid functional like HSE is moderate. Better performance of the GGA+U method clearly indicates that short range coulomb correlation plays more significant role over the non-local Hartree-Fock (HF) exchange in determining the electrical band gap of polymer materials. It is also noticeable that the Hubbard U parameter used for the various polymers under consideration is relatively large, indicating the semi-empirical nature of the GGA+U level of calculations. The present finding will help us design new low band gap polymer through estimating band gap by the GGA+U method and this could be very useful for solar cell research. 相似文献