耦联因子的符号（Abinit-16:能带计算）

能带计算的输入文件如下，需要设置dataset进行两步计算：dataset1是自洽计算，dataset2是非自洽计算：

Crystalline silicon # # Computation of the band structure. # First, a SCF density computation, then a non-SCF band structure calculation. ndtset 2 #Definition of the unit cell acell 3*10.195 # This is equivalent to 10.216 10.216 10.216 rprim 0.0 0.5 0.5 # FCC primitive vectors (to be scaled by acell) 0.5 0.0 0.5 0.5 0.5 0.0 #Definition of the atom types ntypat 1 # There is only one type of atom znucl 14 # The keyword "znucl" refers to the atomic number of the # possible type(s) of atom. The pseudopotential(s) # mentioned in the "files" file must correspond # to the type(s) of atom. Here, the only type is Silicon. #Definition of the atoms natom 2 # There are two atoms typat 1 1 # They both are of type 1, that is, Silicon. xred # This keyword indicate that the location of the atoms 0.0 0.0 0.0 # Triplet giving the REDUCED coordinate of atom 1. 1/4 1/4 1/4 # Triplet giving the REDUCED coordinate of atom 2. #Definition of the planewave basis set ecut 12.0 # Maximal kinetic energy cut-off, in Hartree #Definition of the SCF procedure nstep 20 # Maximal number of SCF cycles diemac 12.0 # Although this is not mandatory, it is worth to # precondition the SCF cycle. #Dataset 1 : usual self-consistent calculation kptopt1 1 # Option for the automatic generation of k points, # taking into account the symmetry nshiftk1 4 shiftk1 0.5 0.5 0.5 # These shifts will be the same for all grids 0.5 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.5 ngkpt1 4 4 4 prtden1 1 # Print the density, for use by dataset 2 toldfe1 1.0d-6 # This value is way too large for most realistic studies of materials #Dataset 2 : the band structure iscf2 -2 getden2 -1 kptopt2 -3 # will have three segments in the band structure nband2 8 ndivsm2 10 # 10 divisions of the smallest of the 3 segments, delimited # by the 4 points defined by kptbounds. kptbounds2 0.5 0.0 0.0 # L point 0.0 0.0 0.0 # Gamma point 0.0 0.5 0.5 # X point 1.0 1.0 1.0 # Gamma point in another cell. tolwfr2 1.0d-12 enunit2 1 # Will output the eigenenergies in eV

获取布里渊区高对称点可以使用Abipy命令:

abistruct.py kpath FILE

处理数据，画出band structure图：

abiopen.py out_DS2_GSR.nc -e

常见问题：

1. symmetry operation error，这个问题困扰好久，最终是通过精确原子位置坐标解决，Abinit对原子位置精确度要求较高，大概小数点后8位，另外会添加chksymtnons 0 参数。
2. 自洽过程不收敛：这个问题也比较麻烦，可通过调节nline参数，diemac，以及nband1来调节收敛性，另外查看mpi文件的nkpt，k点数量，和处理器数量的适配度。
3. 用Abipy画出的能带图一般把Fermi能级和0对齐了。