A¶

ABI: Application binary interface: the functions, types, and calling conventions of libcpmdc as a compiled library. CPMDC_ABI_VERSION and cpmdc_abi_version() number its generations.
BLYP: Becke exchange with Lee, Yang, and Parr correlation, a generalized gradient density functional; the default functional of CPMDParams.

C¶

Calculator: A group of MPI ranks that runs one CPMD calculation with its own communicator and orbitals. Created by cpmdc_bind_calculator().
Cap’n Proto: The serialization format of every message cpmdc reads or writes. capnp encode turns a text message into the binary form.
Cold call: An evaluation that runs CPMD’s full setup and starts the SCF without stored orbitals: the first call of a session, a changed cell, or a re-configured session.
CPMD: Car-Parrinello Molecular Dynamics, the plane-wave density functional code; cpmdc embeds its OpenCPMD distribution.
CPMDParams: The message holding method setup: functional, cutoff, and the deck sections. One per session.
CPMDCSession: The C handle that owns one CPMDParams, a fixed topology, and the results of its last evaluation.

Deck: A CPMD input file of &SECTION ... &END blocks. cpmdc renders one from CPMDParams and hands it to CPMD in memory.
Default build: libcpmdc.so built without OpenCPMD. It evaluates a deterministic reference function so the ABI can be tested anywhere.
DFT: Density functional theory.

ener_com: The OpenCPMD module that holds the energy terms of the last SCF; cpmdc_last_energy_components() copies it.

Feature ID: A stable string naming a capability, such as abi.cpmdc_session_calculate_result or params.inputSections.cpmd.maxIter. Looked up with cpmdc_feature_find().
File route: Running cpmd.x once per force call and exchanging decks and output files through the file system; the alternative to embedding.
fion: OpenCPMD’s array of ionic forces, coor%fion, read by cpmdc after each SCF.
ForceInput: The message holding one geometry: positions, atomic numbers, an optional cell, and output units.

Gauss-Hermite integration: CPMD’s default numerical treatment of the nonlocal pseudopotential projectors, used when KLEINMAN-BYLANDER is not on the pseudopotential file line.

Hockney solver: POISSON SOLVER HOCKNEY, CPMD’s Poisson solver for an isolated system in a box. Added by cpmdc when SYMMETRY 0 has no solver.

Kleinman-Bylander form: A separable form of the nonlocal pseudopotential, selected per species with KLEINMAN-BYLANDER on the *file line, or kleinmanBylander = true in CPMDAtomsPseudopotential.

memfd: An anonymous in-memory file. cpmdc writes the composed deck to one and passes CPMD its /proc/self/fd/N path.
MPI: Message Passing Interface, the library CPMD uses to spread one SCF over several processes (ranks).

NEB: Nudged elastic band, a method that relaxes a chain of images between two minima to find the minimum energy path.

ODIIS: Orbital direct inversion in the iterative subspace, CPMD’s preconditioned DIIS wavefunction optimiser and its default.
OpenCPMD: The open-source CPMD code base at github.com/OpenCPMD/CPMD.

Parent rank: Rank 0 of CPMD’s communicator; it writes CPMD’s output and holds the result the host should use.
PCG: Preconditioned conjugate gradient wavefunction optimiser. PCG MINIMIZE adds a line minimisation along each search direction.
PotentialConfig: A message with one backend arm, such as cpmd, and an optional CommonMethodSpec overlay; read by cpmdc_configure().
PotentialResult: The result message: energy, forces, and the extension fields, in the units ForceInput asked for.
Pseudopotential: A file, such as O_MT_BLYP.psp, replacing the core electrons of an element; found through CPMDC_PSEUDO_DIR.

Reference evaluator: The deterministic function the default build evaluates instead of CPMD.
RESTART.1: CPMD’s binary restart file with orbitals, coordinates, and cell; read and patched by cpmdc-restart.
rgpot: The OmniPotentRPC library that loads potential backends, among them libcpmdc through its CPMDPot frontend.

SCF: Self-consistent field: the iterative optimisation of the orbitals for fixed nuclei that each force call runs.
Stub: libcpmdc_stub.a, a link-only build whose calls all fail and whose cpmdc_available() is 0.

tau0: OpenCPMD’s array of ionic positions in Bohr, coor%tau0, written by cpmdc from each step’s positions.
Topology: The atom count and ordered atomic numbers a session accepts on its first successful step.

Warm call: An evaluation that reuses CPMD’s setup and starts the SCF from the orbitals of the previous call of the same session.