Journal
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Volume 13, Issue 9, Pages 4089-4100Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jctc.7b00295
Keywords
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Funding
- Norwegian Research Council through the CoE [179568/V30]
- Norwegian Research Council through the European Research Council under the European Union Seventh Framework Program through the Advanced Grant ABACUS, ERC Grant [267683]
- Royal Society University Research Fellowship
- Engineering and Physical Sciences Research Council EPSRC [EP/M029131/1]
- Norwegian Research Council [240774]
- EPSRC [EP/M029131/1] Funding Source: UKRI
- Engineering and Physical Sciences Research Council [EP/M029131/1] Funding Source: researchfish
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We study the effects of magnetic fields in the context of magnetic field density-functional theory (BDFT), where the energy is a functional of the electron density p and the magnetic field B. We show that this approach is a worthwhile alternative to current-density functional theory (CDFT) and may provide a viable route to the study of many magnetic phenomena using density-functional theory (DFT). The relationship between BDFT and CDFT is developed and clarified within the framework of the fourway correspondence of saddle functions and their convex and concave parents in convex analysis. By decomposing the energy into its Kohn Sham components, we demonstrate that the magnetizability is mainly determined by those energy components that are related to the density. For existing density functional approximations, this implies that, for the magnetizability, improvements of the density will be more beneficial than introducing a magnetic-field dependence in the correlation functional. However, once a good charge density is achieved, we show that high accuracy is likely only obtainable by including magnetic-field dependence. We demonstrate that adiabatic-connection (AC) curves at different field strengths resemble one another closely provided each curve is calculated at the equilibrium geometry of that field strength. In contrast, if all AC curves are calculated at the equilibrium geometry of the field-free system, then the curves change strongly with increasing field strength due to the increasing importance of static correlation. This holds also for density functional approximations, for which we demonstrate that the main error encountered in the presence of a field is already present at zero field strength, indicating that density-functional approximations may be applied to systems in strong fields, without the need to treat additional static correlation.
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