Parameter: isscr

Definition

It is a key control flag, which specifies what kind of impurity Hamiltonian model need to be solved. Usually, the quantum impurity solvers in the iQIST software package only support the Hubbard model/Anderson impurity model. But with the help of the NARCISSUS component, we have several other choices.

Type

Integer

Default value

1

Component

Only for the NARCISSUS component.

Behavior

There are five possible values for the isscr parameters so far:

• isscr = 1, normal Hubbard model/Anderson impurity model ($U$ is static)

• isscr = 2, Holstein-Hubbard model

• isscr = 3, Dynamic screening effect ($U$ is frequency-dependent), palsmon pole model

• isscr = 4, Dynamic screening effect ($U$ is frequency-dependent), ohmic model

• isscr =99, Dynamic screening effect ($U$ is frequency-dependent), realistic materials

When isscr = 1, lc and wc are ignored.

When isscr = 2, lc means the electron-phonon coupling constant $\lambda$, and wc phonon vibration frequency $\omega_{0}$. The dynamical $U$ is built analytically.

When isscr = 3, lc and wc just mean the control parameters $\lambda$ and $\omega^{'}$, respectively. The dynamical $U$ is built analytically.

When isscr = 4, lc and wc just mean the control parameters $\alpha$ and $\omega_{c}$, respectively. The dynamical $U$ is built analytically.

When isscr = 99, wc is ignored and lc means the shift for interaction matrix and chemical potential. The dynamical $U$ is read from the solver.ktau.in file. Please see solver.ktau.in for more details.

Comment

When you want to use the quantum impurity solvers contained in iQIST software package in extended-DMFT calculations, the isscr parameter must be considered.

When isscr = 1, 3, 4, or 99, you can use the combination of improved estimator and orthogonal polynomial technology to measure $G$ and $\Sigma$. In other words, in such cases, the isort parameter can be any values (isort $\in [1,6]$). On the other hand, when isscr = 2, the orthogonal polynomial technology is useful as well ($G$ is accurate), but the improved estimator for $\Sigma$ and vertex function does not work any more! So in this case, you can not setup isort to 4, 5, or 6. See isort parameter for more details.

isscr = 2 is not compatible with the p = 3 bit of the isvrt parameter. Then if you want to study the two-particle Green's function and vertex function of the Holstein-Hubbard model, you can only set the p = 2 bit of the isvrt parameter. Consult isvrt parameter for more details.

Please refer to lc and wc parameters for more details.