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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8404-8412 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical study for diffusional crossing of a tracer through a membrane, where the size of the adsorbing domain (receptor) is time dependent, is presented. A periodic array of absorbing and reflecting domains at the membrane surface was assumed. This model is described by a time-dependent diffusion equation with mixed boundary conditions, where the boundaries are themselves varying with time. Both analytical and numerical methods were employed in order to calculate the total flux of a tracer across the membrane as a function of the oscillation frequency (ω) and amplitude (ε) of the receptor site. The results show an increase in the absorption rate with frequency, reaching a plateau at very high values of ω. The space and time behavior of the diffusing tracer concentration was analyzed, evidencing dephasing effects at high ω which are common to many nonlinear systems where the dynamic response becomes time independent in the high frequency limit. This approach could be useful in studying the anomalous effect of an oscillating electric field on the membrane permeability. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5477-5485 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the present work we have studied the thermal isomerization process of polyacetylene (PA) from the trans-cisoid (TC) and cis-transoid (CT) forms to the trans-transoid (TT) form. We have used the molecular dynamics-modified neglect of diatomic overlap (MD-MNDO) method, which combines a molecular dynamics algorithm with the MNDO approximation. The thermal isomerization mechanism from TC-to-TT form is fully described. In our simulation, starting from the CT form in its ground state and heating the system up to T=450 K, there is no evidence of an isomerization process. However, a model, which simulate the subtraction of some charge from the double bonds of the PA chains, is able to give important insights into the isomerization mechanism from the CT to the TT form. This charge subtraction is essential to induce a CT-to-TC local transformation followed by the TC-to-TT isomerization.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 721-726 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It has been known since the work of March and White that the simplest nonrelativistic density functional theory, namely, the statistical method of Thomas, Fermi, and Dirac, sums subseries of the so-called 1/Z expansion to yield, for heavy neutral atoms, the ground-state energy E= - a0Z7/3+ a1Z2-a2Z5/3+⋅⋅⋅. The term of O(Z5/3) is the Dirac-Slater exchange energy Eexc, and it is of considerable interest to know at what order the correlation energy Ecorr enters this expansion. Dimensional scaling considerations by Kais et al. suggested Ecorr∝Z4/3 in the limit of large Z. Here, attention is focused on whether this can be distinguished empirically from a term of the form (aZ ln Z+bZ) for neutral atoms. If the latter term is correct, then a relationship between Ecorr and the Shannon information entropy can be forged analytically for large atomic number Z in nonrelativistic theory.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 721-726 (1998)
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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