Coulomb singularity: Difference between revisions

Revision as of 09:11, 10 May 2022

In the unscreened HF exchange, the bare Coulomb operator

{\displaystyle V(\vert\mathbf{r}-\mathbf{r}'\vert)=\frac{1}{\vert\mathbf{r}-\mathbf{r}'\vert} }

is singular in the reciprocal space at $q=\vert\mathbf{k}'-\mathbf{k}+\mathbf{G}\vert=0$ :

{\displaystyle V(q)=\frac{4\pi}{q^2} }

To alleviate this issue and improve the convergence of the exact exchange integral with respect to supercell size (or k-point mesh density) different methods have been proposed: the auxiliary function methods^[1], probe-charge Ewald ^[2] (HFALPHA), and Coulomb truncation methods^[3] (HFRCUT). These mostly involve modifying the Coulomb Kernel in a way that yields the same result as the unmodified kernel within the limit of large supercell sizes.

[gygi:prb:86-1] F. Gygi and A. Baldereschi, Phys. Rev. B 34, 4405(R) (1986).

[massidda:prb:93-2] S. Massidda, M. Posternak, and A. Baldereschi, Phys. Rev. B 48, 5058 (1993).

[spenceralavi:prb:08-3] J. Spencer and A. Alavi, Phys. Phys. Rev. B 77, 193110 (2008).

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@@ Line 3: / Line 3: @@
 V(\vert\mathbf{r}-\mathbf{r}'\vert)=\frac{1}{\vert\mathbf{r}-\mathbf{r}'\vert}
 </math>
-is singular in the reciprocal space at <math>\mathbf{q}=\mathbf{k}'-\mathbf{k}+\mathbf{G}=0</math>:
+is singular in the reciprocal space at <math>q=\vert\mathbf{k}'-\mathbf{k}+\mathbf{G}\vert=0</math>:
 :<math>
 V(q)=\frac{4\pi}{q^2}