Diffusion Monte Carlo Calculations for Rare-earths: Applying the Long-range Corrected Scheme to Minnesota M06 Functional

Nagat Elkahwagy,K R Mahmoud,S M A Maize,Atif Ismail

doi:10.13189/ujpa.2016.100304

Nagat Elkahwagy, K R Mahmoud + Show 2 more

Open Access

https://doi.org/10.13189/ujpa.2016.100304

Copy DOI

Abstract

By employing the diffusion Monte Carlo (DMC) method, we test the success of the unpublished long-range corrected M06 (LC-M06) functional, compared to LC-BLYP functional, in improving the calculations of the ground and excited states energies for some 4f- and 5f-rare-earths at different values of the range separation parameter μ. It is found that LC-M06 functional performs well for both the ground and the excited states of 4f-lanthanides. In addition, our results reveal that the optimal value of μ for the ground state lies between 0.40-0.50 a.u. while a smaller optimal value μ =0.35 a.u. is found for the excited states. However, LC-BLYP ground and excited states results at the optimal value of μ seem to be the best for 5f-actinides.

Highlights

A computational study of rare-earths has received much attention in the past few decades
We make use of CRENBL ECP basis set [15] for all elements except for La atom where CRENBS ECP basis set is being used which proved to be successful for the calculations. Both the ground and excited states energies have been calculated within a diffusion Monte Carlo (DMC) framework
The electronic excitation involves a promotion of an electron with a change of spin from 6s → 5d and 7s → 6d for lanthanides and actinides respectively

Summary

Introduction

A computational study of rare-earths has received much attention in the past few decades. Among the most successful methods in treating the strongly correlated electrons systems is the diffusion Monte Carlo (DMC) method which explicitly includes electron-electron correlation effects. It scales well with system size, with the computational cost increasing as the cube of the number of electrons. The conventional hybrid functionals (which combine a pure exchange functional in DFT with HF exchange integral in a constant ratio) are not usually regarded as a fundamental approach to solve all DFT problems probably since these functionals contains only short-range HF exchange so the long-range asymptotic behavior still remains incorrect.

Methods

Results

Conclusion