# *AMFI¶

Note

We highly recommend to use the *XAMFI module rather than the present *AMFI module as highlighted by the numerical examples provided in [Knecht2022].

Specification of the AMFI, RELSCF directives.

The AMFI program of B.Schimmelpfennig serves for calculating spin-orbit contributions to various quasirelativistic two-component Hamiltonians. Its important part is the independent scalar atomic code - RELSCF (named as AT34), which is providing atomic orbital coefficients for the AMFI mean-field summation.

The user may control not only the extent of the output, but also provide here some parameters for the RELSCF code. Note that closed/open-shell HF-SCF code gives both the nonrelativistic and the spin-free second-order Douglass-Krol-Hess SCF energies, which can be compared with DIRAC results.

RELSCF is using only decontrated basis sets restricted to occupied shells only; for example, if you set some spdf-basis for a DIRAC BSS+AMFI run of Magnesium (12 electrons), RELSCF will use, for the sake of computational effectivity, this basis set with only s- and p- exponents.

## .PRNT_A¶

Print level for AMFI calculations.

*Default:*

```
.PRNT_A
0
```

## .PRNT_S¶

Print level for the RELSCF part.

*Default:*

```
.PRNT_S
0
```

## .MXITER¶

Maximum number of iterations in RELSCF.

*Default:*

```
.MXITER
50
```

## .AMFICH¶

Set up an artificial charge of the calculated system which has effect only on the AMFI mean-field summation(s). This does not change the electronic occupation for the DIRAC SCF procedure.

The reason is that AMFI-attached scalar relativistic Hartree-Fock SCF module might not be converging for certain high-spin open-shell atoms (like Pt,Yb), what is anyway expected for a single-determinant code. A small positive charge (+1, +2) usually helps to get converged molecular orbitals of given atom with a negligible change in results due to AMFI mean-field contribution. The AMFI mean-field contributions are large for core shells, but small for valence orbitals.

In the case of polyatomic systems the overall AMFI-charge is proportionally distributed over individual atoms and rounded to the closest integer value.

Example:

```
.AMFICH
+1
```

The user can check the mean-field occupation/charge of each handled atom in the AMFI/RELSCF output, together with the RELSCF convergence status.

## .NOAMFC¶

Discard selected centers from AMFI calculations. Related the
.BSS keyword, whose
numerical value *axyz* must have y=0 (i.e. ‘spin-free’ from the DIRAC
BSS side, while AMFI provides SO terms of first order in potential).

First line specifies how many atoms are neglected, the second line gives centers to be omitted. Number for each center of calculated system is determined in the DIRAC output file.

Infinite order scalar terms “from the end”, and the (one-electron) spin orbit term (SO1) from AMFI. Centers 1 and 3 are neglected.

```
.BSS
5009
.NOAMFC
2
1 3
```

## .ONLSCF¶

Stop DIRAC calculation after RELSCF program has finished. The
(converged) AO coefficients are written to the file *RELSCF_COEF* and
can be used to restart from.

This may be useful in combination with the keyword .AMFICH, *i.e.*
the user may first run the RELSCF step for an atom with an artificial
charge.

The obtained coefficients can then be used to start the RELSCF step for the neutral atom for which otherwise one would not obtain convergence.

Input example:

```
.ONLSCF
```