ExafsArchitect

ExafsArchitect is an automation tool designed to streamline the creation and evaluation of advanced molecular and materials models by systematically varying coordination geometries for spectroscopic simulation. By acting as a structural bridge to high-powered engines like FEFF and ORCA, it eliminates the tedious manual editing of input files, allowing researchers to rapidly analyze structural effects in Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Spectroscopy (XAS), and X-ray Emission Spectroscopy (XES) profiles.

This technical guide outlines how to construct, manipulate, and evaluate advanced materials models using the ExafsArchitect framework. Core Architecture and Workflow

ExafsArchitect uses a systematic coordination-variation paradigm. Instead of relying on static atomic snapshots, it generates grids of structural permutations.

[Define Absorbing Center] ──> [Map Coordination Spheres] ──> [Parametrize Ligand Vectors] │ [Spectroscopic Evaluation] <── [Automated Input Generation] <─── Batch Coordinate Shifts

The underlying mechanism maps structural changes directly to spectral responses. This helps resolve local ambiguities in disordered systems, catalysts, and complex biomolecules. Step-by-Step Modeling Guide 1. Initializing the Primary Absorbing Center

Every advanced materials model begins with defining the X-ray absorbing atom.

Import initial Cartesian or fractional coordinates from crystallographic databases (such as .cif or .xyz formats).

Designate the core absorbing node (e.g., a transition metal center like Pt, Fe, or Cu).

Establish the core bounding box to segregate the active cluster from long-range crystalline constraints. 2. Defining Ligand Matrices and Coordination Spheres

Once the core absorber is set, you must map the surrounding environment:

Group neighboring scattering atoms into specific coordination spheres based on distance radial cuts.

Define rigid or semi-rigid ligand groups (such as imidazole rings, water clusters, or halide networks).

Assign localized coordinate systems to these ligands, relative to the absorbing center, to prepare them for translation or rotation. 3. Parametrizing Geometric Variations

The primary strength of ExafsArchitect is its ability to build multi-dimensional structural grids.

Radial Distortion ®: Define a range of bond length variations (e.g., scanning an M-O bond from 1.90 Å to 2.15 Å in steps of 0.01 Å).

Angular Distortion (θ, φ): Introduce tilting, twisting, or bending angles to simulate Jahn-Teller distortions or asymmetric coordination sites.

Occupancy Fluctuation: Vary the structural composition to model mixed-ligand architectures or intermediate states.

Ligand (Position A) <─── [Radial Shift ®] ───> Absorbing Center (M) ⟪ [Angular Shift (θ)] ⟫ Ligand (Position B) 4. Automated Input Deck Generation

Manually writing input files for dozens of structural permutations is prone to errors. ExafsArchitect automates this entirely:

For FEFF: The tool generates a series of feff.inp files, automatically populating the ATOM cards with updated coordinates, while maintaining control parameters like RPATH, NLEG, and exchange-correlation potentials.

For ORCA: It formats quantum chemical input files (.inp), establishing correct spin states, charge states, functionals, and basis sets needed for subsequent XES or XAS transitions. 5. Batch Execution and Spectral Extraction

Run the generated job arrays through your chosen computing environment:

Feed the batch inputs into FEFF or ORCA to simulate individual spectrum curves (χ(k) or intensity vs. energy).

Use ExafsArchitect’s evaluation routines to parse the output logs.

Extract crucial parameters—such as mean free path values, scattering amplitudes, and phase shifts—across the entire structural matrix. Analysis: Correlating Structure with Spectroscopy

Evaluating the output grid involves tracking how specific geometric changes alter your experimental data matches: Structural Parameter Primary EXAFS Impact Visual Indicators in χ(k) / FT Bond Length Extension ® Phase change in scattering paths Radial peaks shift to higher R-space values Coordination Number (N) Amplitude modification Proportional scaling of peak height in Fourier Transform Angular Tilting (θ) Multi-body scattering suppression Changes in outer-shell peak intensities (3.0 – 5.0 Å) Best Practices for High-Fidelity Models

Apply Constraints Wisely: Avoid physically impossible atom overlaps by setting explicit minimum distance thresholds between moving ligand groups.

Reconcile Multi-Body Paths: When changing angles, ensure your multi-body scattering path calculations in FEFF are deep enough (NLEG = 4 or higher) to capture focusing effects accurately.

Validate with DFT: Use ORCA calculations within the workflow to verify that the highly distorted structural models on your grid remain energetically stable or chemically feasible.

If you need help setting up your workflow, please let me know which spectral method you are focusing on (EXAFS, XANES, or XES), your absorbing element, and which simulation engine (FEFF or ORCA) you plan to use. ExafsArchitect download | SourceForge.net