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2001 (2)
2000 (1)
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    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 
3Author    Prasad Durga, Devesh Ojha, V.G K M Kumar, PisipatiRequires cookie*
 Title    Molecular Organization in a Nematogen: PBPCN -A Computational Analysis Based on Quantum Mechanics  
 Abstract    A computational analysis has been carried out to determine the configurational preference of a pair o f 4'-n-pentyloxy-4-biphenylcarbonitrile (PBPCN) molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Modified Rayleigh-Schrödinger perturbation theory along with 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. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements o f molecular pair have been considered. It has been observed that the molecule has a strong preference for stacking through a particular face, while the other configurations, such as stacking through the other face, in-plane and terminal interactions show, in general, an aligned structure along molecular axis. The results are discussed in the light o f experimental as well as other theoretical observations. 
  Reference    Z. Naturforsch. 56a, 730—734 (2001); received September 7 2001 
  Published    2001 
  Keywords    PBPCN, Nematogen, Interaction Energy, Computer Simulation 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0730.pdf 
 Identifier    ZNA-2001-56a-0730 
 Volume    56