Glossary

Short definitions for OpenPFC and PFC simulation vocabulary. Deeper design detail is in architecture.md and halo_exchange.md. Use this page as a hub: other guides link here for jargon; follow links out to tutorials and ADRs.

Term

Meaning

Phase field crystal (PFC)

Semi-atomistic modeling: periodic order parameters approximate crystal density; used for microstructure, defects, and large-scale evolution.

Domain

Global description of the grid: dimensions, spacing, origin, periodicity (kernel/data). Note: World is a deprecated alias for Domain.

Decomposition

Partition of the domain across MPI ranks; each rank owns an inbox of local samples.

Inbox / outbox

Real-space samples owned by a rank (inbox) and complex outbox layout after real-to-complex FFT (sizes differ due to symmetry).

Halo (ghost cells)

Overlapping boundary layers exchanged between neighbors for finite differences or stencils.

In-place vs separated halos

In-place: ghosts stored in the same array as interior (good for FD-only). Separated: ghosts in face buffers so the interior stays FFT-safe — see halo_exchange.md.

Spectral method

Spatial operators applied in Fourier space (FFT forward → multiply → inverse FFT); primary path in OpenPFC.

Finite difference (FD)

Spatial derivatives on the grid with halos; coexists with spectral workflows when layouts match the docs.

Abstract spatial operators (direction)

Roadmap: choose spectral vs FD for gradients/Laplacians behind a unified interface where supported — see adr/0002-gradient-operators-fd-vs-spectral.md.

HeFFTe

Library for distributed FFT; OpenPFC’s FFT backend selection goes through HeFFTe (FFTW / CUDA / ROCm).

Kernel / runtime / frontend

Kernel: portable abstractions. Runtime: CPU/CUDA/HIP execution and FFT. Frontend: optional JSON/TOML App, I/O helpers — see architecture.md.

Model

Your physics: fields, time step, spectral or FD operators (kernel/simulation).

Simulator

Orchestrates Model, Time, FieldModifier (IC/BC), ResultsWriter.

FieldModifier

Applies initial or boundary updates each step or at startup.

SimulationContext

Small bundle (MPI comm, rank-0) passed with Model to modifiers for rank-aware I/O; see simulation_context.hpp and app_pipeline.md.

App<Model>

Frontend entry point that loads JSON/TOML and builds a session (pfc::ui::App).

plan_options

HeFFTe FFT planner settings (backend, reshape algorithm, pencils, GPU-aware MPI, …), usually a JSON object or TOML [plan_options] — see tutorials/fft_heffte_plan_options.md.

saveat

Time between periodic result writes in the spectral Time object; ≤ 0 disables the default JSON binary-writer path (spectral_app_config_reference.md).

BinaryWriter / binary field files

MPI-IO raw output per timestep; no file header — see binary_field_io_spec.md.

GPU-aware MPI

MPI implementation that can pass device buffers; required for some CUDA/HIP + HeFFTe paths — see INSTALL.LUMI.md, tutorials/gpu_app_quickstart.md.

VTK (.vti)

XML image data for visualization; produced by VTKWriter in code — see tutorials/vtk_paraview_workflow.md.

See also