ORDERING OF A THERMOTROPIC MESOGEN AT PHASE TRANSITION TEMPERATURE — A STATISTICAL APPROACH BASED ON QUANTUM MECHANICS

2005 ◽  
Vol 04 (03) ◽  
pp. 803-810 ◽  
Author(s):  
DURGA PRASAD OJHA
Keyword(s):  
Phase Transition ◽  
Quantum Mechanics ◽  
Transition Temperature ◽  
Phase Transition Temperature ◽  
Intermolecular Forces ◽  
Dielectric Medium ◽  
Theoretical Support ◽  
Molecular Ordering ◽  
Complete Neglect ◽  
Schrödinger Perturbation

The molecular ordering of a thermotropic mesogen, 4-alkenyl bicyclohexylnitrile (ALKBCHN), has been carried out on the basis of quantum mechanics and intermolecular forces. The evaluation of atomic charges and dipole moment at each atomic centre has been done through the Complete Neglect Differential Overlap (CNDO/2) method. The configurational energy has been computed using the Rayleigh-Schrodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration in a dielectric medium (i.e. non-interacting and non-mesogenic solvent, benzene) at phase transition temperature (364.7 K) using the Maxwell–Boltzmann formula. It has been observed that in dielectric medium the energies/probabilities are redistributed and there is a considerable rise in the probability of interactions, although the order of preference remains the same. An attempt has been made to develop a new and interesting model of mesogen in a dielectric medium. The present article offers a theoretical support to the experimental observations.

Smectogenic Behaviour of 7O.6 at it's Phase Transition Temperature: A Computational Analysis Reprint request to

2001 ◽  
Vol 56 (12) ◽  
pp. 873-878
Author(s):  
Durga Prasad Ojha ◽  
Devesh Kumar ◽  
V. G. K. M. Pisipati
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Perturbation Method ◽  
Phase Transition Temperature ◽  
Computational Analysis ◽  
Atomic Charge ◽  
Configurational Energy ◽  
Schrödinger Perturbation ◽  
Atomic Centre

Abstract A computational analysis has been carried out to determine the configurational preference of a pair of Ar-(4-n-heptyloxybenzylidine)-4-hexylaniline (70.6) molecules with respect to translatory and orien­ tational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atom ic dipole components at each atomic centre of the molecule. The configurational energy has been com­ puted using the modified Rayleigh-Schrödinger perturbation method. The obtained energies were used to calculate the probability of each configuration at phase transition temperature, using Maxwell-Boltz-mann's formula. The flexibility of various configurations has been studied in terms of variations of the probability due to small departures from the most probable configuration. The results are discussed in the light of experimental as well as other theoretical observations. The smectogenic character of the molecule has been correlated with the parameters introduced in this paper.

Nematogenic Behaviour of a Cyano-Compound Using Quantum Mechanics and Computer Simulations

2001 ◽  
Vol 56 (3-4) ◽  
pp. 319-325 ◽  
Author(s):  
Durga Prasad Ojha
Keyword(s):  
Quantum Mechanics ◽  
Perturbation Method ◽  
Computer Simulations ◽  
Atomic Charge ◽  
Intermolecular Forces ◽  
Relative Order ◽  
Configuration Energy ◽  
Molecular Ordering ◽  
Schrödinger Perturbation ◽  
Atomic Centre

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 of 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].

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