Recent advancement in material engineering has led to the development of materials with strongly correlated electrons that will be of great importance in various applications. For instance, they exhibit excellent physical properties including superconductivity and magnetism effects that have attracted significant attention of researchers. However, in order to unleash their full potential, a thorough understanding of the strongly correlated electron system is highly desirable. Generally, the correlated electrons of the system are described based on the on-site Coulomb and exchange interactions between them and the on-site interaction parameters for the description. As such, several methods have been developed for the efficient determination of the on-site interaction parameter.
Among the available methods, constraint density functional method that basically determines the on-site interaction parameter by varying the correlated electron numbers is widely preferred. In conjunction with other techniques such as linearized muffin-tin orbital method, calculation of electron structures of the varying number of the correlated electrons is possible. Unfortunately, it is impossible to use this constraint density functional method together with pseudoptential and projector augmented wave methods. Therefore, researchers have been looking for an alternative and have identified the inclusion of empirical on-site interaction parameters as a promising solution for calculation of the electron structure in strongly correlated electron systems.
To this note, Dr. Tomoyuki Hamada at Research and Development Group together with Dr. Takahisa Ohno from the National Institute of Material Science developed a new constraint density functional method for investigating the strongly correlated electron systems electronic structures. Fundamentally, the technique entailed the densityfunctional+U projector augmented wave or pseudopotential method. Furthermore, they calculated the constraint density functional energy by consistently varying the number of the correlated electrons, and calculated the on-site interaction parameter for these electrons from the energy, to be such that it determined the electronic structure and vice versa. They purposed to improve the theoretical investigation of the electronic structure of materials. Their study is currently published in the research journal, Condensed Matter.
In brief, the authors commenced their work by cross-examining the electronic structure of strongly correlated electronic systems. Next, the developed method was used to determine the on-site interaction parameter and compared it to that determined empirically. Additionally, they assessed the feasibility of determining the electronic structure using the first principles. Eventually, they compared and contrasted the effectiveness of this method to that of self-consistent linear response calculation technique.
The authors observed that the newly developed technique enabled determination of the on-site interaction parameter exhibiting the ability to further determine the electronic structures of the strongly correlated electronic systems. Additionally, this technique was observed to be as efficient as the self-consistent linear response method. However, it is more advantageous as it involves less calculation cost.
In summary, the research team successfully developed a novel technique for determining the self-consistent U values. To actualize their study, they confirmed the effectiveness of this technique by using it to determine the on-site interaction parameter of correlated electrons for iron oxide and neodymium sesquioxide. This was attributed to the fact that it enabled first principle determination of electron structures together with the high parallel computing efficiency. Owing to its efficiency and fewer calculation costs, it will advance studies of large and complex strongly correlated electronic systems. The developed technique is going to be implemented in a first princiles calculation program, PHASE (Platform for High-performance Atomic Structure Environment) a research term including the authors has been developing, in the near future.
Hamada, T., & Ohno, T. (2019). A new constraint DFT technique for self-consistent determination of U values. Journal of Physics: Condensed Matter, 31(6), 065501.
PHASE Consortium (2019). PHASE/0 2019.01 (National Institute of Materials Science, Tsukuba, 2019): https://azuma.nims.go.jp/Go To PHASE