DIPOL: Difference between revisions

Revision as of 05:39, 10 August 2021

DIPOL = [real array]

Description: specifies the center of the cell in direct lattice coordinates with respect to which the total dipole-moment in the cell is calculated.

The center of the cell w.r.t. which the total dipole-moment in the cell is calculated is specified as

DIPOL=R_x R_y R_z

where R_x, R_y and R_z are given in direct lattice coordinates.

Mind: the calculation of the dipole (IDIPOL=1-4) requires a definition of the center of the cell, and results might differ for different positions. You should use this option only for surfaces and isolated molecules. In this case, use the center of mass for the position. Additionally, mind that for surfaces, only the component normal to the surface is meaningful.

The main problem is that the definition of the dipole 'destroys' the translational symmetry, i.e., the dipole is defined as

{\displaystyle \int ({\mathbf r}-{\mathbf R}_{\rm center}) \rho_{\rm ions+valence}({\mathbf r}) d^3 {\mathbf r}. }

Now, this makes only sense if $\rho_{\rm ions+valence}$ drops to zero at some distance from $\mathbf R_{\rm center}$ . If this is not the case, the values are extremely sensitive with respect to changes in $\mathbf R_{\rm center}$ .

Note: If the flag 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).

Related Tags and Sections

NELECT, EPSILON, IDIPOL, LDIPOL, LMONO, EFIELD, Monopole, Dipole and Quadrupole corrections

Examples that use this tag

Contents

@@ Line 11: / Line 11: @@
 '''Mind''': the calculation of the dipole ({{TAG|IDIPOL}}=1-4) requires a definition of the center of the cell, and results might differ for different positions.
 You should use this option only for surfaces and isolated molecules.
-In this case use the center of mass for the position (for surface only the component normal to the surface is meaningful).
+In this case, use the center of mass for the position. Additionally, mind that for surfaces, only the component normal to the surface is meaningful.
-The main problem is that the definition of the dipole 'destroys' the translational symmetry, i.e. the dipole is defined as
+The main problem is that the definition of the dipole 'destroys' the translational symmetry, i.e., the dipole is defined as
 :<math>
@@ Line 20: / Line 20: @@
 Now, this makes only sense if <math>\rho_{\rm ions+valence}</math> drops to zero at some distance from <math>\mathbf R_{\rm center}</math>. If this is
-not the case, the values are extremely sensible with respect to changes in <math>\mathbf R_{\rm center}</math>.
+not the case, the values are extremely sensitive with respect to changes in <math>\mathbf R_{\rm center}</math>.
-'''Note''': If the flag 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).
+'''Note''': If the flag 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).
 == Related Tags and Sections ==