The Developments And Applications Of First-principles Software Package ABACUS

In recent years,first-principles methods based on density functional theory are playing an increasingly important role in the calculation and prediction of biology,chemistry,and condensed matter physics materials.On the one hand,due to the de-velopment of supercomputer hardware and the progress of numerical algorithms,the process of self-consistent solution of ground state is faster and faster.On the other hand,it is also because of the decades of developement of density functional theory it-self,such as the continuously optimization of mature method of plane wave base and the continuous development of local atomic orbital algorithm,etc.This makes it possible to simulate complex systems accurately on a larger scale.First-principles computing soft-ware is very important as a platform for carrying the development of algorithms and as an important tool for solving practical scientific problems.The research group of the author has developed a first-principles computing software package,Atomic-orbital Based Ab-initio Computation at USTC(ABACUS),which is mainly based on numerical atomic orbital algorithm and compatible with plane wave base algorithm from scratch.Its advantage is that the numerical atomic orbital algorithm can calculate a larger system,and the computational efficiency for thousands or even tens of thousands of systems is 1?2 orders of magnitude higher than the plane wave base algorithm.During the doctoral study,the author of this paper focuses on the development and improvement of the ABACUS computing software and applid the software to study specific scientific problems.The research focuses on how to realize the stress calcula-tion and the spin-orbit coupling calculation under the numerical atomic orbital basis set,complete the theoretical derivation and improve the efficiency in the process of program implementation.The dynamic properties and fuel cycle mechanism of fusion covering materials were studied by using this software and the magnetic structure of triangular lattice was studied by using first principles method.The main contents and achievements of this paper are as follows:In the first chapter,the basic knowledge of the ground state density functional theory is briefly reviewed,and the ABACUS scientific calculation software based on the first principles method is introduced in the plane wave basis set and the numerical atomic orbital basis set respectively.We developed the first-principle molecular dynamics and its realization method are introduced in the second chapter.We used this function to explore the dynamic properties of liquid tin as a fusion covering material in the plasma surface environment and studied the diffusion process of fuel deuterium in the plasma surface environment.Furthermore,the excellent properties and application potential of lithium-tin eutectic as a fusion cladding material are studied and pointed out,and the process of fuel deuterium forming deuterium gas molecules in the eutectic for fuel recovery is emphasized,and the catalytic effect of lithium during formation of D2 moleculars in the eutectic is pointed out.In chapter 3,we developed a method for structural stress calculation based on nu-merical atomic orbital basis set.The correctness of the method is verified by energy finite-difference method.We show that the convergence of stress calculation for en-ergy truncation is superior to that for plane wave basis set method.We developed a spin-orbit coupling method based on plane wave basis set and nu-merical atomic orbital basis set respectively,and introduced the implementation method in Chapter 4.The correctness of the method was verified by comparing the energy band structure.In the fifth chapter,we used the first principles method to simulate the triangle grid material NaYbS2 and NaYbO2 magnetic structure,and under considering only the nearest neighbor spin exchange model fitting the exchange parameters.According to the exchange of parameters for the phase diagram of the classic monte-carlo simulation,we pointed out that there is no quantum spin liquid if only considering the nearest-neighbor exchange action.The Z2 vortex state appears after the addition of appropriate secondary neighbor interaction,which may cause the quantum spin liquid state.In the sixth chapter,the developments of ABACUS software and outlooks are in-troduced,and the contribution of the author in these developments is summarized.