QE计算能带详细教程

说明：以二维InSe原胞为例，QE版本：，赝势：SSSP。

1.结构优化

通过Materialsstudio2018的建模功能切出二维InSe原胞，如图所示，并导出为格式。

二维InSe原胞

2、QE输入文件结构

QE的结构优化主要使用的是模块，该模块包含非常多的输入参数，建议在计算过程中逐步学习，无需一次性学完所有命令，即使学完也是徒劳，因为几乎无法记住。

结构优化在QE中是比较诟病的一个地方，优化速度非常慢，对于大体系实现结构优化是非常慢的，如果计算的体系包含较多的原子，建议使用VASP。QE结合EPW计算材料的与声子有关的性质比较合适，且这类计算一般不需要建立超胞，能够达到计算目的。总之，根据计算的任务和目的合理选择第一性原理计算软件是比较明智的。

2.1模块输入文件结构

CONTROL/SYSTEM/ELECTRONS/[IONS/][CELL/]ATOMIC_SPECIESXMass_XPseudoPot_XYMass_YPseudoPot_YZMass_ZPseudoPot_ZATOMIC_POSITIONS{alat|bohr|crystal|angstrom|crystal_sg}{if_pos(1)if_pos(2)if_pos(3)}K_POINTS{tpiba|automatic|crystal|gamma|tpiba_b|crystal_b|tpiba_c|crystal_c}if(gamma)nothingtoreadif(automatic)nk1,nk2,nk3,k1,k2,k3if(notautomatic)nksxk_x,xk_y,xk_z,wk[CELL_PARAMETERS{alat|bohr|angstrom}v1(1)v1(2)v1(3)v2(1)v2(2)v2(3)v3(1)v3(2)v3(3)][OCCUPATIONSf_inp1(1)f_inp1(2)f_inp1(3)f_inp1(10)f_inp1(11)f_inp1(12)f_inp1(nbnd)[f_inp2(1)f_inp2(2)f_inp2(3)f_inp2(10)f_inp2(11)f_inp2(12)f_inp2(nbnd)]][CONSTRAINTSnconstr{constr_tol}constr_type(.)constr(1,.)constr(2,.)[constr(3,.)constr(4,.)]{constr_target(.)}][ATOMIC_FORCESlabel_1Fx(1)Fy(1)Fz(1)..label_nFx(n)Fy(n)Fz(n)]

2.2二维InSe原胞结构优化输入文件

CONTROLcalculation='vc-relax',!vc-relax|relaxrestart_mode='from_scratch',!normalusedprefix='InSe',!prepedtoinput/outputfilenamespseudo_dir='../pseudo/',!directorycontainingpseudopotentialfilesoutdir='../tmp/',!input,temporary,outputfilesarefoundinthisdirectoryforc_conv_thr=1d-5,!forcesconvergencethreshold1d-03/SYSTEMibrav=0!Bravais-latticeindexnat=4!numberofatomsintheunitcellntyp=2!numberoftypesofatomsintheunitcellecutwfc=60.0,!kineticenergycutoff(Ry)forwavefunctionsecutrho=720.0,!Kineticenergycutoff(Ry)forchargedensity/ELECTRONSmixing_beta=0.7,!mixingfactorforself-consistencyconv_thr=1d-8,!Convergencethresholdforselfconsistency1d-6/IONSion_dynamics='bfgs',!Specifythetypeofionicdynamics/CELLcell_dynamics='bfgs',!Specifythetypeofdynamicsforthecellpress=0.0,!press_conv_thr=0.5,!Convergencethresholdonthepressureforvariablecellcell_dofree=2Dxy,!for2Dmaterials/CELL_PARAMETERS{angstrom}!specifythestructure4.08360004430.00000000000.0000000000-2.04180002213.53650137720.00000000000.00000000000.000000000025.3775005341ATOMIC_SPECIES!__pbe_ATOMIC_POSITIONS{crystal}K_POINTSautomatic12121000

2.3结构优化的经验总结

模块用于结构优化时，对于体系的对称性非常敏感，也就是QE自身不会寻找体系的对称性，只能依靠手动输入体系的对称性，这点与VASP相比是非常欠缺的，因为VASP是可以自己寻找对称性的。对于二维InSe原胞，有对称性与无对称性的结构优化使用时间相差了近５倍。

查看优化所用时间

|tail-n1

输入对称性

PWSCF:4

没有输入对称性

PWSCF:21

对于离子的受力，一般使用准牛顿迭代算法

ion_dynamics='bfgs'

pwscf模块做结构优化时，对于二维材料无需重新编译软件，即可做到不优化真空层，这点比VASP方便，具体设置如下

cell_dofreeCHARACTERDefault:'all'Selectwhichofthecellparametersshouldbemoved:'all':allaxisandanglesaremoved'ibrav':allaxisandanglesaremoved,butthelatticebutberepresentablewiththeinitialibravchoice'x':onlythexcomponentofaxis1(v1_x)ismoved'y':onlytheycomponentofaxis2(v2_y)ismoved'z':onlythezcomponentofaxis3(v3_z)ismoved'xy':onlyv1_xandv2_yaremoved'xz':onlyv1_xandv3_zaremoved'yz':onlyv2_yandv3_zaremoved'xyz':onlyv1_x,v2_y,v3_zaremoved'shape':allaxisandangles,keepingthevolumefixed'volume':thevolumechanges,keepingallanglesfixed((1)changes)'2Dxy':onlyxandycomponentsareallowedtochange'2Dshape':asabove,keepingtheareainxyplanefixed'epitaxial_ab':fixaxis1and2whileallowingaxis3tomove'epitaxial_ac':fixaxis1and3whileallowingaxis2tomove'epitaxial_bc':fixaxis2and3whileallowingaxis1tomoveBEWARE:ifaxisarenotorthogonal,,editsubroutineinit_dofreeinfileModules/cell_

3、结构自洽计算

3.1输入文件

CONTROLcalculation='scf',restart_mode='from_scratch',prefix='InSe',pseudo_dir='../pseudo/',outdir='../tmp/',/SYSTEMibrav=0nat=4ntyp=2ecutwfc=60.0,ecutrho=480.0,/ELECTRONSmixing_beta=0.7,conv_thr=1d-8,/CELL_PARAMETERS{angstrom}4.0819105670.0000000000.000000000-2.0409552833.5350382470.0000000000.0000000000.00000000025.377500534ATOMIC_SPECIES__pbe_ATOMIC_POSITIONS{crystal}K_POINTSautomatic12121000

$$ecutwfc

grep-e'kinetic-energycutoff'-e!$ecutwfc|\awk'/kinetic/{ecutwfc=$(NF-1)}/!/{printecutwfc,$(NF-1)}'_vs_ecutwfc

done

3.2ecutwfc测试

forecutwfcin50556065707580;do
self-consistentcalculation$kpointsEOFCONTROLcalculation='scf',restart_mode='from_scratch',prefix='InSe',pseudo_dir='../pseudo/',outdir='../test_tmp/',/SYSTEMibrav=0nat=4ntyp=2ecutwfc=70,ecutrho=840,/ELECTRONSmixing_beta=0.7,conv_thr=1d-8,/CELL_PARAMETERS{angstrom}4.0819105670.0000000000.000000000-2.0409552833.5350382470.0000000000.0000000000.00000000025.377500534ATOMIC_SPECIES__pbe_ATOMIC_POSITIONS{crystal}K_POINTSautomatic$kpoints$kpoints1000EOF
$$kpoints
echo-e"$kpoints\c"_vs_kpointsgrep!$kpoints|\awk'/!/{print$(NF-1)}'_vs_kpoints
done

测试结果：

kpoints

3.4结构自洽计算总结

通过对ecutwfc和kpoints的测试，我们选定ecutwfc的值为80Ry，kpoints的值为８８1，用这个值返回去重新优化结构和自洽，然后开始计算下面的性质。

4、能带计算

4.1输入文件

CONTROLcalculation='bands',restart_mode='from_scratch',prefix='InSe',pseudo_dir='../pseudo/',outdir='../tmp/',verbosity='high',/SYSTEMibrav=0nat=4ntyp=2ecutwfc=80.0,ecutrho=960.0,nbnd=26,/ELECTRONSmixing_beta=0.7,conv_thr=1d-8,/CELL_PARAMETERS{angstrom}4.085963663-0.0000000000.000000000-2.0429818323.5385483310.0000000000.0000000000.00000000025.377500534ATOMIC_SPECIES__pbe_ATOMIC_POSITIONS{crystal}K_POINTScrystal_b40.50.00.0100!M0.00.00.0100!G0.333330.333330.0100!K0.50.00.0100!M

4.2后处理文件文件

bandsprefix='InSe',outdir='../tmp/',filband='',lsym=.true./

4.3画能带图的后处理程序

Reading26bandsat301k-pointsfilewithrepresentationsnotcompatiblewithbandsRange:-16.45005.4820eVEmin,Emax-44high-symmetrypoint:0.50000.28870.0000high-symmetrypoint:0.00000.00000.0000high-symmetrypoint:0.33330.57730.0000high-symmetrypoint:0.50000.28870.0000outputfile(gnuplot/xmgr)bandsingnuplot/outputfile(ps)deltaE,referenceE(fortics)2-1.5444

说明：QE自带的画图程序画出的能带图几乎无法直接用于文章中，因此这步处理意义不大。可以直接使用计算出的文件，通过origin等专业的绘图软件绘制能带图。

能带图计算结果：