# QSGW Transverse spin susceptibility

This tutorial describes how to compute the transverse spin susceptibilty $\chi^\pm(\mathbf{q},\omega)$ within the Rigid Spin Approximation (RSA) using QSGW wave functions.

By making the RSA, an effective Stoner I can be inferred from a sum rule, avoiding the need to compute a two-particle vertex. The RSA is a good approximation for local-moment systems such as Fe where the spin is large and rotates rigidly. The approximation degrades as magnetic moments become small, when local moments begin to flex as they rotate.

This tutorial is written for elemental Fe, building on the basic QSGW tutorial for Fe.

### Preliminaries

Executables blm, lmfa, and lmf are required and are assumed to be in your path; similarly for the QSGW script lmgwsc; and the binaries it requires should be in subdirectory code2. For graphics, this tutorial uses the plbnds and fplot utilities.

When a text editor is required, the tutorial uses the nano text editor.
To view the postscript file, this document assumes you are using the apple-style open command.

### Command Summary

1. LDA self-consistency (starting from init.fe)

### Tutorial

This tutorial starts in a working directory where you have completed the basic QSGW tutorial for Fe.

Thus it assumes you have the following files in your working directory

Tutorial NEEDS COMPLETION

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