4.3 Iron magnetism: search states, do not trust one seed

These are unexecuted teaching inputs and starting models. Original diagrams are schematics, not calculated results. Validate version-specific syntax, licensed or authorized data, numerical convergence and the scientific model before using this workflow.

4.3.1 Model, units and provenance

PW cutoffs and energies use Ry, common force output uses Ry/bohr, and pressure uses kbar. Geometry cards state their coordinate units. Different executables have distinct grammars and time-unit conventions.

Shared inputs, conventions and evidence

Original schematic: Iron magnetism: search states, do not trust one seed. No numerical results are claimed.

4.3.2 Unexecuted inputs and explicit deltas

Use the accompanying instructions to identify the parent calculation and placement of every delta; a snippet is not automatically a standalone input. Preserve all blank-line and file-provenance requirements.

4.3.2.1 Input block 1

! New Fe species, one Fe at crystal 0 0 0; new prefix/outdir.
! SYSTEM changes:
ibrav=3, A=2.86, nat=1, ntyp=1,
nspin=2, starting_magnetization(1)=0.5,
occupations='smearing', smearing='mv', degauss=0.02
! ATOMIC_SPECIES
Fe 55.845 Fe.PBE.UPF

4.3.3 Worked investigation

4.3.3.1 Intuition and prerequisites

Spin-polarized DFT may converge to different local electronic minima. A magnetic initialization helps select a basin but is not a measured final moment. Use a verified Fe PBE pseudopotential and a bcc primitive cell. The starting lattice 2.86 Å and seed 0.5 below are illustrative. First converge the metallic k mesh and smearing for the selected Hamiltonian.

4.3.3.2 Original delta from Al-base

See input block 1 above.

4.3.3.3 Checks, pitfalls and exercise

Use a seed with magnitude below one here to avoid ambiguity across version-dependent interpretations of large starting_magnetization values. A zero net moment can describe either a nonmagnetic state or an antiferromagnet; inspect local/spatial magnetization. Compare energy differences only at matched geometry, sampling and smearing convention. Exercise: track moment versus volume with fresh seeds and identify whether discontinuities are physical candidates or switching between unconverged branches.