VASP偶极校正及功函数的计算

具体参考（转载）：VASP 偶极校正及功函数的计算

VASP偶极修正相关参数

• IDIPOL
  • IDIPOL switches on  corrections to the total energy
• LDIPOL
  • LDIPOL switches on corrections to the potential and forces
  • The user must also ensure that the cell is sufficiently large to determine the dipole moment with sufficient accuracy. If the cell is too small, the charge might slash through the vacuum, causing very slow convergence. Often convergence improves with the size of the supercell
• DIPOL
  • DIPOL sets the center of the net charge distribution: DIPOL=R_center in direct coordinates, The dipole (moment ) is then defined as

• • If DIPOL is not set, VASP determines, where the charge density averaged over one plane drops to a minimum and calculates the center of the charge distribution by adding half of the lattice vector perpendicular to the plane where the charge density has a minimum (this is a rather reliable approach for orthorhombic cells)

Comments on DIPOL

不同的R_center，可能会得到不能的结果，具体如何设置，网上大致有三种说法：几何中心、质心和净电荷中心

对于几何中心和质心，可以在MS上通过Centroid来确定，默认得到的是质心，如需要纯几何中心，则需要将IsWeighted设置为No.

对于表面和孤立分子体系，vaspwiki建议设为质心. 对于净电荷中心，这个似乎不好先验确定. DIPOL为空时，VASP会默认寻找净电荷分布中心，但是自洽计算收敛非常慢，甚至不收敛，特别对于高收敛标准的EDIFF，经常会跑散（前期有收敛趋势，能达到较低的收敛标准，而到了一定程度会增大发散！）因此建议先使用质心或者几何中心来计算，完了比较下两者功函数的计算结果，有时候未必有差异！经验上，建模时可让Slab原子居中，R_center=0.5 0.5 0.5

偶极修正的原理

偶极修正的原理是在Slab真空层中间引入一层planar dipoles [PhysRevB.46.16067]

提取真空和费米能级

grep vacuum OUTCAR  #提取真空能级
grep E-fermi OUTCAR #提取费米能级

功函数：WF=E_vac−E_F