3DSCalculator

Live tool: https://maximeremenko.github.io/3DSCalculator/

A browser-based forward diffuse-scattering calculator. It computes the three-dimensional diffuse intensity I(h,k,l) in reciprocal space directly from atomistic structure files — RMCProfile .rmc6f configurations, LAMMPS data files, or unified structure HDF5 — and visualizes the result as interactive 3D isosurfaces, 3D slice planes, and 2D slice maps. Everything runs client-side in the browser: structure files never leave your machine.

Documentation

The docs/ directory contains the full documentation set (live entry point: https://maximeremenko.github.io/3DSCalculator/docs/):

• User Guide — UI walkthrough and workflow.
• Examples — worked examples with the shipped benchmark files.
• Theory — the equations behind the calculator.
• Supplementary — backend provenance and scattering-table families.
• Bibliography — formal references.
• Troubleshooting — common issues and fixes.

Features

• Input formats: RMCProfile .rmc6f (with the spin .cfg and .dat of magnetic RMC), LAMMPS data files (.data / .lmp / .lammps, including atom_style spin), unified structure HDF5 (.h5 / .hdf5), and Scatty spin or atom files (.txt), loaded via drag-and-drop or the file picker (several files at once). Several configurations of one system selected together (RMC runs, Monte Carlo or MD snapshots) are averaged. Intensity data as h k l I [σ] lists (Scatty _sc_list.txt, Spinteract single-crystal data) load straight into the viewers.
• Comparison with data: a calculation is fitted to loaded intensity data (scale, flat or linear-in-|Q| background, weights 1/σ², as in Spinteract), with R_wp, R and χ² per degree of freedom. The views switch between the scaled calculation and the data, which share one color range, and a difference map in a diverging color map.
• Compute backends: the default, wgpuNUFFT type-1 (WebGPU), evaluates the uniform h,k,l grid as a type-1 NUFFT on the GPU (bundled wgpu-web), with all phases prepared in fp64 and every run spot-checked against exact sums. The other engines are the type-3 WebGPU path (Type-3 + webgpufft), CPU FFT (type3NufftCpu), a CPU f64 NUFFT (type3NufftCpuDirect), and an exact CPU f64 direct sum for small validation grids. If WebGPU is unavailable the app falls back to the CPU FFT backend automatically; large grids on the WebGPU paths run in chunks.
• Interface: a Setup panel (structure, reciprocal grid, scattering, computation) with a pinned Compute button (Ctrl+Enter), three resizable and maximizable views, and a View panel for slice, color, 3D and export tools; light and dark themes; example structures one click away (including paramagnetic MnO, as random spins and at 160 K as 8 Monte Carlo snapshots, LAMMPS spin data for bcc Fe, and the Pt chains of KCP, whose independent Peierls waves give diffuse sheets); a drawer layout for tablets and phones.
• Magnetic scattering (neutrons): magnetic-only or nuclear + magnetic intensity from Scatty spin files, RMCProfile magnetic configurations (moments and form factors from the .dat MAGNETISM block) and LAMMPS spins. It uses the perpendicular projection |M⊥|², Brown ⟨j0⟩/⟨j2⟩ form factors for 155 ions, and optional ideal-paramagnet subtraction. A species table sets the form factor, C2 and moment of each magnetic species. It is validated against J. A. M. Paddison's Scatty on MnO and spin ice.
• Modulated and incommensurate structures (optional tools, shown on request): a displacive wave, spin-density wave or helix with any wavevector q, applied to the loaded structure; satellites come out at G ± q with the box's finite-size width.
• Radiation types: neutron (fast and grouped-exact models), X-ray (Waasmaier table), and electron scattering (neutral-atom tables: Lobato, Peng, Doyle, Weickenmeier, Kirkland; ionic Peng model with user-specified valences).
• Calculation options: average-lattice subtraction, normalization controls, Laue symmetrization (Scatty's 12 Laue classes), optional 3D smoothing (Lanczos or Chebyshev filter), and an experimental per-element filter.
• Visualization: interactive Plotly 3D isosurface and 3D slice-plane views, plus a 2D slice heatmap with three slice modes — axis-aligned slices, arbitrary normal-plane slices, and volume-average slabs. Log/linear scaling, six colormaps, adjustable display levels, and a detachable slice window.
• Exports: .dat (h k l intensity columns), .json, unified diffuse-data HDF5 (.h5), ParaView .vtk (structured HKL grid), Gaussian .cube (ChimeraX/ParaView), 2D slice SVG and CSV, 3D plane/iso SVG snapshots, and standalone interactive Plotly HTML files of the 3D views.

Precision note: the WebGPU paths and the CPU FFT path use fp32 arithmetic. On the shipped examples the type-1 backend stays within about 1e-6 of the peak intensity of exact sums. type3NufftCpuDirect runs the NUFFT in fp64, with an accuracy set by the tolerance (1e-9 by default); it is not an exact sum. For critical scientific checks, compare against the Exact sum backend on a small grid.

Getting Started

Open index.html in a modern browser. All local modules load through plain script tags (no local fetch or workers), so opening the file directly from disk (file://) works in practice. From disk, the browser does not let the page read Examples/ itself, so the example buttons load the compressed copies in Examples/embedded (written by tools/make_embedded_examples.py). The exception is PMN (30 MB), which opens the file dialog. A local web server is the most reliable route:

python -m http.server

then browse to http://localhost:8000/index.html.

Notes:

• Internet is required on first load for the CDN scripts: the WebGPU-NUFFT type-3 kernels and WebGPU smoothing (jsDelivr) and Plotly (cdn.plot.ly, loaded on demand). HDF5 support (h5wasm) and the type-1 engine (wgpu-web) are bundled locally in js/. The NUFFT and FFT libraries are pinned (WebGPU-NUFFT v0.1.0, WebGPU-FFT commit fa45c93), so results do not change when those repositories move on.
• The WebGPU backend requires a WebGPU-capable browser (e.g. current Chrome or Edge). Other browsers automatically use the CPU FFT backend.

Open Examples in the Structure card and pick one (or load your own structure), check the h,k,l grid, and press Compute diffuse (Ctrl+Enter).

Examples

Three benchmark .rmc6f configurations ship in Examples/:

File	Description
LiFeO2.rmc6f	Chemical-order benchmark with diffuse manifold plus 1/2(111) condensation.
CaTiO3.rmc6f	Displacement benchmark with overlapping rod-like and breathing-related diffuse features.
PMN_300k.rmc6f	Relaxor benchmark for anisotropic diffuse features and complex slice exploration.

Magnetic examples sit in Examples/magnetic/ (MnO spin configurations as Scatty files and in RMCProfile's format) and Examples/lammps/ (LAMMPS atom_style spin data for bcc Fe and a skyrmion film, written by tools/make_lammps_examples.py). Modulated structures sit in Examples/modulation/ (the Pt chains of KCP and a bcc Cr box for the Modulation tools, written by tools/make_modulation_examples.py). Examples/README.md describes each file.

Tests

The tests/ directory holds Node tests for the shared JavaScript modules (unified HDF5 I/O and the diffuse amplitude core). Run them from the repository root with Node 22 or newer:

node --test

Provenance

This repository was extracted (with full git history, via git filter-repo) from the MaximEremenko/Utilities monorepo, where the tool lived under RMCProfileUtilities/Diffuse_Scattering/. The shared modules js/unified_hdf5.js and js/h5wasm.js are vendored from that monorepo's Format_Converter component; h5wasm is NIST-developed software (see js/h5wasm-LICENSE.txt). js/wgpu_web.js is the standalone build of wgpu-web 0.3.2 attached to the MaximEremenko/wgpuNUFFT v0.3.2 release (commit 69a3da9, built by wgpu-web/build_standalone.py in its CI). Companion tools from the Utilities collection remain in the monorepo and are linked from the documentation.

Scope

This tool is a forward diffuse-scattering calculator and visualization surface. It does not perform the MOSAIC inverse reconstruction workflow; the MOSAIC paper is referenced in the docs for scientific benchmark context only.

License

Apache License 2.0 — see LICENSE. The vendored h5wasm bundle carries its own NIST license notice in js/h5wasm-LICENSE.txt; the vendored wgpu-web bundle is Apache-2.0 (js/wgpu_web-LICENSE.txt).