# Fleur crystal field workflow

• Current version: 0.2.0

• String to pass to the WorkflowFactory(): fleur.cfcoeff

• Workflow type: Scientific workchain

• Aim: Calculate 4f Crystal field coefficients

Import Example:

from aiida_fleur.workflows.cfcoeff import FleurCFCoeffWorkChain
#or
WorkflowFactory('fleur.cfcoeff')


## Description/Purpose

Calculates the 4f crystal field coefficients for a given structure using the method. described in C.E. Patrick, J.B. Staunton: J. Phys.: Condens. Matter 31, 305901 (2019).

This method boils down to the formula

$B_{lm} = \sqrt{\frac{2l+1}{4\pi}} \int^{R_{MT}}\! dr r^2 V_{lm}(r)n_{4f}(r)$

where $$V_{lm}(r)$$ is the potential of the surroundings of the 4f site and $$n_{4f}(r)$$ is the spherical charge density of the 4f state. The potential is calculated using one of two options:

1. Calculate the potential of an analogue structure, where the 4f atom is replaced by a ytrrium atom.

2. Calculate the potential from the system including the 4f atom directly.

This is done by first calculating the converged charge density for the 4f structure and if used the analogue structure with the FleurScfWorkChain. Then a subsequent calculation is done to extract the potentials/charge density. The calculation of the formula above is done after with the CFCalculation tool in masci-tools.

## Input nodes

The table below shows all the possible input nodes of the SCF workchain.

name

type

description

required

scf

namespace

Inputs for the SCF workchain including the 4f atom

no

orbcontrol

namespace

Inputs for the Orbcontrol workchain including the 4f atom

no

scf_rare_earth_analogue

namespace

Inputs for the SCF workchain with the 4f atom replaced with the analogue

no

wf_parameters

Dict

Settings of the workchain

no

One of the scf or orbcontrol input nodes is required.

### Workchain parameters and its defaults

• wf_parameters: Dict - Settings of the workflow behavior. All possible keys and their defaults are listed below:

# -*- coding: utf-8 -*-
'element': '',                          # detemines for which element to calculate
# the crystal field coefficients
'rare_earth_analogue': True,            # True if analogue calculation should be used
'analogue_element': 'Y',                # Which element to use for the analogue structure
'replace_all': True,                    # Whether to replace all atoms for the analogue in one structure
'soc_off': True,                        # if True the socscale is set to 0.0 for the 4f site
'convert_to_stevens': True              # if True the coefficients are converted to the stevens convention
# A_lm<r^l>


## Returns nodes

The table below shows all the possible output nodes of the SCF workchain.

name

type

comment

output_cfcoeff_wc_para

Dict

results of the workchain

output_cfcoeff_wc_potentials

XyData

XyData with the calculated potentials

output_cfcoeff_wc_charge_densities

XyData

XyData with the calculated charge densities

TODO

## Error handling

In case of failure the SCF WorkChain should throw one of the exit codes:

Exit code

Reason

230

Invalid workchain parameters

231

Invalid input configuration

235

Input file modification failed.

236

Input file was corrupted after modifications

345

SCF workchain failed

451

Orbcontrol workchain failed

452

FleurBaseWorkChain for CF calculation failed

If your workchain crashes and stops in Excepted state, please open a new issue on the Github page and describe the details of the failure.

TODO

TODO

TODO