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Low Field NMR Spectra for Molecules from FHI-aims and SPINACH

This tutorial provides a step-by-step guide on how to generate low-field NMR spectra using data from FHI-aims combined with the MATLAB-based SPINACH (Spectral Interpretation using Spin Dynamics) package. Specifically, we will cover the process for simulating Zero to Ultra Low Field (ZULF) and Spin-Lock Induced Crossing (SLIC) spectra, utilizing the NAO-J-n basis sets. This guide includes detailed instructions on obtaining relevant magnetic resonance parameters (such as J-couplings and shieldings) from FHI-aims, then processing these outputs in SPINACH to generate spectra.

SPINACH

SPINACH (Spectral Interpretation using Spin Dynamics) is an advanced simulation package written in MATLAB for modeling magnetic resonance spectra, including NMR, ESR, and low-field techniques. SPINACH solves the quantum mechanical spin dynamics of coupled systems, which is necessary to simulate NMR spectra that consider all relevant magnetic interactions (J-couplings, shielding, etc.).

  • Language Requirement: SPINACH is written in MATLAB. Although Octave can run basic MATLAB scripts, it is not currently compatible with the complex features and optimizations used in SPINACH.

  • Further Information: SPINACH documentation and code are available on its official website.

  • ZULF provides high-resolution spectra by relying on heteronuclear J-couplings, which remain observable even at zero magnetic field.

  • SLIC focuses on homonuclear coupling interactions at low magnetic fields. It does not require heteronuclei, making it effective for proton-only systems (H-H systems).

Both techniques enhance structural identification at low fields, each with unique advantages. With ZULF, heteronuclear couplings offer high spectral dispersion and sensitivity to molecular structure, while SLIC provides characteristic spectral patterns based on proton interactions, useful for analyzing smaller molecules.

This tutorial is built based on Zero-field NMR and millitesla-SLIC spectra for > 200 molecules from density functional theory and spin dynamics.

Objectives of This Tutorial

  • Calculate NMR parameters such as J-couplings and shielding tensors with FHI-aims.
  • Generate ZULF and SLIC spectra using SPINACH.
  • Illustrate and interpret low-field spectra.

Prerequisites

To make the most of this tutorial, you should:

  • Have a basic understanding of how to run FHI-aims, as it assumes you are working with an optimized geometry from a previous FHI-aims calculation. If you're new to the code or need a refresher, we recommend reviewing the Basics of Running FHI-aims tutorial before proceeding. This will ensure you are well-prepared and can follow along easily.
  • Have access to FHI-aims and MATLAB (with the SPINACH library installed).
  • The low-field NMR spectra were simulated using SPINACH library version 2.9.2 in MATLAB (R2024b).