Energy Stability Calculations for ultrathin multilayers: a comparison between various models for calculating correlation energy and exchange

Abstract

The computer codes for Theoretical solid state chemistry (free and paid) are becoming ever more versatile and many computing strategies can be used, such as parallel comparison and vector comparison using many computers in a network, etc. But generally, we use electronic structure calculation models, using Hartree-Fock, to obtain state properties. These include the calculation of thermodynamic properties, with DFT (Density Functional Theory) calculations using a large number of available functions. Therefore, it is very important to understand the implementation and operation of the DFT routine using these codes to determine the available parameters. The growth in spintronics, together with frequent news about advances in quantum computation, has resulted in DMS (Diluted Magnetic Semiconductors) being studied intensively. In this new technology that emerges, the spin of the bearer contains the information that will be used. So, we cannot merely use local charge density as a parameter to calculate interactions between bearers. To solve this, we used LSDA (Local Spin Density Approximation), which uses local spin density, performed based on DFT (Density Functional Theory). As there are too many LSDA parameterizations for exchange correlation potential, we decided to implement some of the most widely used ones and compare the results in order to reach a conclusion regarding which parameterization is most coherent according to our study. LSDA was studied first. This approximation is an efficient and accurate plan to answer the problem of many electrons in a crystal using DFT. Over the years, there has been great progress regarding approximations and perhaps LSDA is not one of the best anymore, but it always shows a safe calculation and its simple application does not depend on big computers. The Generalized Gradient Approximations (GGAs) appeared to correct the approximation problems, which are discussed in Perdew-Burke-Ernzerhof (PBE 96). This approximation was constructed to maintain the correct characteristics of LSDA and add other formal properties. Nowadays, PBE 96 is the most widely-used GGA in theoretical solid state chemistry calculations and this correlation is given by correlation energy of the electron gas. PBE 96 is the functional unit that implements a bond on its functional form through the fixing of one of its parameters. In 2006, WC_GGA (Wu-Cohen) appeared, created by Zhigang Wu and R.E. Cohen. Its parameterization is better for solids when compared with others such as LSDA and PBE 96. The last parameterization is PBESol - GGA (Perdew, et al 2008), which minimizes the dependence on error cancellation between exchange and correlation. One approach to lattice properties is to use a modified function, specially created for solid expansion of the exchange gradient across a wide range of density gradients. With the emergence of a new class of compounds, nanostructured multilayers in F/M/F form appeared where F is a ferromagnetic multilayer and M is a metallic film. In this paper, in addition to describing the parameterizations, we will construct a case study by applying the electronic structure calculations to this new class of compounds, thus creating a scientific paper worthy of publication in the aforementioned book.