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2001 (2)
2000 (3)
1Author    DurgaPrasad OjhaRequires cookie*
 Title    Molecular Ordering of 4-Acetyl-2 / -Nitrobiphenyl - A Computational Analysis  
 Abstract    The molecular ordering of some biphenyl derivatives like 4-acetyl-2'-nitrobiphenyl (ANBP), 4-nitro-2-biphenylamine (NBPA) and 4-acetyl-3'-chlorobiphenyl (ACBP) has been examined using basic con-cepts of quantum mechanics and intermolecular forces. The CNDO/2 method has been employed to compute the net atomic charge and atomic dipole components at each atomic centre. The modified Ray-leigh-Schrödinger perturbation theory along with the multicentred-multipole expansion method has been employed to evaluate long-range interactions while a '6-exp' potential function has been assumed for short-range interactions. Accuracies upto 0.1 A in translation and 1° in rotation have been achieved. Probability of occurrence of a particular configuration has been calculated using MB-statistics. On the basis of stacking and in-plane interaction energy calculations, all possible geometrical arrangements between molecular pairs have been considered and a most favorable configuration of pairing has been obtained. A comparative picture of molecular parameters like total energy, binding energy, total dipole moment etc. has been given. An attempt has been made to develop a molecular model correlated with the liquid crystalline property exhibited by this class of molecules. 
  Reference    Z. Naturforsch. 55a, 918—922 (2000); received April 3 2000 
  Published    2000 
  Keywords    Biphenyl Derivatives, CNDO/2 Method, Interaction Energy, MB-Statistics 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0918.pdf 
 Identifier    ZNA-2000-55a-0918 
 Volume    55 
2Author    Prasad Durga, B. Ojha, V.G K M Raja Rajeswari, PisipatiRequires cookie*
 Title    Molecular Ordering of a Nematic Liquid Crystal in a Dielectric Medium  
 Abstract    A computational analysis of the molecular ordering of 4-(4'-ethoxyphenylazo) phenyl hexanoate (EPPH) has ben carried out on the basis of intermolecular interaction energy calculations. The CNDO/2 method has been employed to evaluate the net atomic charge ad atomic dipole moment components at each atomic centre of the molecule. A modified Rayleigh-Schrödinger perturbation theory alongwith a multicentered-multipole expansion method has been employed to evaluate long-range intermolecular interactions, while a "6-exp" potential function has been assumed for short-range interactions, and cor-responding probabilities have been calculated in a dielectric medium (benzene) using the Maxwell-Boltzmann formula. Further, the flexibility of various configurations has been studied in terms of vari-ations of the probability due to departure from the most probable configuration. All possible geometri-cal arrangements between molecular pairs have been considered during stacking, in-plane and terminal interactions, and the most favourable configuration of the paring has been obtained. It has been observed that in a dielectric medium the probabilities are redistributed and there is a considerable rise in the prob-ability of interactions although the order of preference remains the same. An attempt has been made to explain the nematogenic behaviour of liquid crystals and thereby develop a molecular model for liquid crystallinity. Results have been discussed in the light of those obtained for other nematogens like EPPV [4-(4'-ethoxyphenylazo) phenyl valerate] and DPAB [4-4'-di-n-propoxy-azoxybenzene], 
  Reference    Z. Naturforsch. 55a, 929—935 (2000); received November 3 2000 
  Published    2000 
  Keywords    CNDO/2 Method, Intermolecular Interactions, Statistical Analysis, Computer Simulation 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0929.pdf 
 Identifier    ZNA-2000-55a-0929 
 Volume    55 
3Author    DurgaPrasad OjhaRequires cookie*
 Title    Nematogenic Behaviour of a Cyano-Compound Using Quantum Mechanics and Computer Simulations  
 Abstract    Using quantum mechanics and intermolecular forces, the molecular ordering of a nematogenic cya-no-compound, 5-(frans-4-ethylcyclohexyl)-2-(4-cyanophenyl)-pyrimidine (ECCPP), has been exam­ ined. The CNDO/2 method has been employed to evaluate the net atomic charge and the dipole mo­ ment components at each atomic centre of the molecule. The configuration energy has been computed using the modified Rayleigh-Schrödinger perturbation method at intervals o f 1Ä in translation and 10P in rotations, and corresponding probabilities have been calculated using Maxwell-Boltzmann statistics. The flexibility of various configurations has been studied in terms of the variation of the probability due to small departures from the most probable configuration. All possible geometrical arrangements between a molecular pair have been considered during stacking, in-plane and terminal interactions, and the most favourable configuration of pairing has been obtained. An attempt has been made to under­ stand the behaviour of the molecules in terms of their relative order. The results have been compared with those obtained for other nematogens like DPAB [4,4'-di-n-propoxy-azoxybenzene] and EMBAC [ethyl 4-(4'-methoxybenzylidene amino) cinnamate]. 
  Reference    Z. Naturforsch. 56a, 319—325 (2001); received February 6 2000 
  Published    2001 
  Keywords    ECCPP, CNDO/2 Method, Intermolecular Forces, Computer Simulation 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0319.pdf 
 Identifier    ZNA-2001-56a-0319 
 Volume    56 
4Author    DurgaPrasad OjhaRequires cookie*
 Title    Nematogenic Behaviour of EPPV in a Dielectric Medium. A Theoretical Study  
 Abstract    4-(4/-ethoxyphenylazo) phenyl valerate (EPPV) is a nematic liquid crystal, which shows a nematic mesophase at 352 K and becomes an isotropic melt at 401 K. A theoretical study o f the molecular order­ ing has been carried out on the basis of intermolecular interaction energy calculations. The CNDO/2 method has been employed to compute the net atomic charge and atomic dipole components at each atom­ ic centre of the molecule. Modified Rayleigh-Schrödinger perturbation treatment has been employed to calculate the interaction energy between a molecular pair. The probability of the occurrence of a partic­ ular configuration in a dielectric medium has been calculated using the Maxwell-Boltzmann formula. The flexibility of various configurations has been studied in terms of the variation of the probability due to a small departure from the most probable configurations. On the basis of stacking, in-plane and terminal interactions, all possible geometrical arrangements between a molecular pair have been considered, and the most favourable configuration of pairing has been obtained. An attempt has been made to explain the nematogenic behaviour of liquid crystals based on the parameters introduced in this paper. 
  Reference    Z. Naturforsch. 56a, 371—375 (2001); received December 4 2000 
  Published    2001 
  Keywords    CNDO/2 Method, Interaction Energy, Statistical Distribution 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0371.pdf 
 Identifier    ZNA-2001-56a-0371 
 Volume    56 
5Author    DurgaPrasad OjhaRequires cookie*
 Title    Molecular Ordering in Liquid Crystalline EMBAC. A Quantum Mechanical Study  
 Abstract    Molecular ordering in a liquid crystal, ethyl 4-(4'-methoxybenzylidene amino) cinnamate (EMBAC) has been studied by intermolecular interaction energy calculations. The CNDO/2 method has been employed to compute the atomic charge and atomic dipole at each atomic centre. The modified Rayleigh-Schrödinger perturbation theory along with the multicentered-multipole expansion method have been employed to evaluate the long-range intermolecular interactions, while a '6-exp' potential function has been assumed for the short-range interactions. On the basis of stacking, in-plane, and terminal interac-tion energy calculations all possible geometrical arrangements of a molecular pair have been considered, and the most favourable configuration of the pair has been obtained. Molecular parameters like total ener-gy, binding energy and total dipole moment have been given. Results are discussed in the light of those obtained for the nematogens 4-(4'-ethoxyphenylazo) phenyl valerate (EPPV) and 4,4'-di-n-propoxy-azoxybenzene (DPAB). An attempt is made to explain the liquid crystalline behavior of these liquid crys-tals and thereby develop a molecular model for liquid crystallinity. 
  Reference    Z. Naturforsch. 55a, 923—928 (2000); received September 28 2000 
  Published    2000 
  Keywords    Liquid Crystal, Multicentered-multipole, CNDO/2 Method, Intermolecular Interactions, EMBAC 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0923.pdf 
 Identifier    ZNA-2000-55a-0923 
 Volume    55