The Development Of First-principles Software Package ABACUS And Its Application In Two-dimensional Materials

Nowadays,with the rapid development of the computer technology,the first-principles method based on density functional theory(DFT)has been increasingly used in con-densed matter physics,chemistry,biology,medicine,and materials science.Since 2006,our group started to develope the first-principle software package ABACUS based on the numerical atomic orbital basis sets.The advantage is that this programme can calculate larger systems,up to thousands or even tens of thousands of atoms,which im-proves the upper limit by 1?2 orders of magnitude compared to plane wave basis set.It performs well in the calculation of biomolecules,surfaces,defects,and disordered systems.In addition,the novel features of plasmons in two-dimensional materials,such as graphene,has also attracted our attention.Compared to metallic materials,the plasmon frequency in graphene can be continuously tuned from the infrared to terahertz range by varying the doping level,and also has.the characteristics of strong field localization and low energy loss simultaneously.Since the traditional semi-classical method ignores the quantum and non-local effects,it is not suitable for accurate calculations.Using linear response time-dependent density functional theory method(LR-TDDFT)can solve this problem.This thesis is divided into seven parts:In the first chapter,we briefly introduce the Hartree-Fork method and the ground state density functional theory.In the second chapter,we mainly discuss the major steps of electronic structure calculations in ABACUS and especially describe the applications of symmetry and the conjugate gradient method in structure optimization.In the third chapter,we systematically benchmark the performance of ABACUS on various systems such as molecules,solids,surfaces and defects.The results verified the reliability of this program.In the fourth chapter,we introduce the module of linear response time-dependent density functional theory(LR-TDDFT)developed in ABACUS.In the fifth chapter,we apply our LR-TDDFT implementation to calculate the plas-mon dispersion relationship and lifetime of graphene and graphene/hBN heterojunction.For Dirac plasmons in graphene,the dispersion relation should be(?)and quasi-linear below and above the Fermi wave vector,respectively.The lifetime should be infinite below 0.8kF where kF is the Fermi wave vector.For ? plasmons in graphene,the dis-persion relation should be(?)when q is small,where Eg,M is the energy gap at the M point in the Brillouin zone,and the lifetime is finite at all q values.In the sixth chapter,we briefly discuss the calculation of the dielectric constant under the linear response time-dependent density functional theory framework.In Appendix A,we calculate the hyperferroelectris LiBO3(B=V,Nb,Ta,Os).By means of model Hamiltonian analysis,we clarify the origin of hyper ferroelectricity—the short-range interaction.This work provides a useful guidance in searching for novel hyperferroelectrics.