Parameter: issun

Definition

Key control flag, it is used to determine the symmetry of bands/orbitals.

Type

Integer

Default value

2

Component

ALL

Behavior

There are two possible values for the issun parameter so far:

• issun = 1, the bands are not symmetrized.

• issun = 2, the bands are symmetrized according to symmetry matrix symm.

The quantum impurity solvers will symmetrize the relevant physical quantities according to the issun parameter.

Comment

There is still one question. What's the symmetry matrix and where is it?

In fact, we should call it symmetry vector, instead of symmetry matrix. It is an integer vector whose size is exact norbs. The quantum impurity solvers will use it to perform symmetrization. Let's suppose this vector is called symm. For example, there is a 5-band model, the symmetry vector is as follows:

symm(01) = 1
symm(02) = 2
symm(03) = 3
symm(04) = 4
symm(05) = 4
symm(06) = 4
symm(07) = 5
symm(08) = 5
symm(09) = 5
symm(10) = 1

Guess which orbitals are degenerated?

ehh, the orbitals 1 and 10, since symm(01) and symm(10) are all 1. Similarly, the orbitals 4, 5, and 6 are degenerated. The orbitals 7, 8, and 9 are degenerated as well.

Yes, you are right. The quantum impurity solvers will consider that those orbitals which have the same symmetry number (the element of symm) are degenerated.

By default, the elements in symm vector are 1. In other words, if issun = 2, all of the orbitals are degenerated. If you want to re-assign the degenerated orbitals, you can edit the solver.eimp.in file. See solver.eimp.in for more details.