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Exchange constants in molecule-based magnets derived from density functional methods.

Thomas, I. O. and Clark, S. J. and Lancaster, T. (2017) 'Exchange constants in molecule-based magnets derived from density functional methods.', Physical review B., 96 (9). 094403.


Cu(pyz)(NO3)2 is a quasi-one-dimensional molecular antiferromagnet that exhibits three-dimensional long-range magnetic order below T N = 110 mK due to the presence of weak interchain exchange couplings. Here, we compare calculations of the three largest exchange coupling constants in this system using two techniques based on plane-wave basis-set density functional theory: (i) a dimer fragment approach and (ii) an approach using periodic boundary conditions. The calculated values of the large intrachain coupling constant are found to be consistent with experiment, showing the expected level of variation between different techniques and implementations. However, the interchain coupling constants are found to be smaller than the current limits on the resolution of the calculations. This is due to the computational limitations on convergence of absolute energy differences with respect to basis set, which are larger than the interchain couplings themselves. Our results imply that errors resulting from such limitations are inherent in the evaluation of small exchange constants in systems of this sort, and that many previously reported results should therefore be treated with caution.

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Publisher statement:Reprinted with permission from the American Physical Society: Thomas, I. O., Clark, S. J. & Lancaster, T. (2017). Exchange constants in molecule-based magnets derived from density functional methods. Physical Review B 96(9): 094403 © 2017 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:16 August 2017
Date deposited:05 September 2017
Date of first online publication:01 September 2017
Date first made open access:05 September 2017

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