FDVIB is a C++17 finite-difference vibration controller for Quantum ESPRESSO. It generates Cartesian displacements, runs pw.x, constructs a Gamma-point dynamical matrix from central force differences, and prepares input for QE's dynmat.x.

FDVIB supports:

• frozen-environment local harmonic calculations for selected atoms in a periodic system;
• isolated-molecule rigid-rotor harmonic-oscillator (RRHO) thermochemistry;
• compact Molden output for normal-mode visualization;
• harmonic and frequency-floor treatments of low positive frequencies.

It is not a replacement for ph.x, q2r.x, Phonopy, or full periodic phonon calculations.

• CMake 3.12 or later
• A C++17 compiler
• Quantum ESPRESSO pw.x and dynmat.x

cmake -S . -B build
cmake --build build -j

The executable is written to build/fdvib. To install it:

cmake --install build --prefix "$HOME/.local"

Version tags produce a prebuilt Linux x86_64 archive on the GitHub Releases page. The binary targets glibc 2.17 or newer and statically links libstdc++ and libgcc; it is therefore suitable for CentOS/RHEL 7 and most newer glibc distributions. The archive also contains the reference documentation, license, and configuration examples. Quantum ESPRESSO is not bundled.

tar -xzf fdvib-X.Y.Z-linux-x86_64-glibc-2.17.tar.gz
install fdvib-X.Y.Z-linux-x86_64-glibc-2.17/bin/fdvib "$HOME/.local/bin/fdvib"

A calculation directory contains:

scf.in       Quantum ESPRESSO SCF input
fdvib.in     displacement and execution settings
thermo.in    thermochemistry settings

The QE input must use ibrav=0, ATOMIC_POSITIONS angstrom, and CELL_PARAMETERS angstrom. It must also define calculation='scf', tprnfor=.true., and an outdir.

Configuration templates are available in examples/local and examples/gas. Gas calculations require selected_atoms='all', an explicit spin multiplicity, and consistent QE spin settings. Gas RRHO thermochemistry removes exactly five rigid-body modes for a linear molecule or six for a nonlinear molecule and rejects any imaginary frequency remaining in the true vibrational modes. Gas pressure is specified with pressure_atm, where 1 atm = 101325 Pa; gas calculations do not use zero_tolerance_cm1.

From the calculation directory:

fdvib prepare fdvib.in
fdvib run fdvib.in
fdvib analyze fdvib.in

cd fdvib/results
dynmat.x -in dynmat.in > dynmat.out
cd ../..

fdvib modes fdvib/results
fdvib thermo fdvib/results

prepare creates positive and negative displacements for each selected Cartesian coordinate. run executes the corresponding pw.x calculations. analyze forms and symmetrizes the finite-difference Hessian and writes the QE dynamical matrix and dynmat.in. Execution of dynmat.x remains an explicit QE post-processing step. Generated local and gas inputs both use asr='no'; rigid-body modes are excluded later according to molecular degrees of freedom.

Existing QE output and Molden files are not overwritten. Dataset settings used by analyze are loaded from immutable snapshots created by prepare.

The result directory contains:

fdvib/results/
  system.dynG
  system.freq.out
  system.mold
  dynmat.in
  fdvib.in.reference
  thermo.in
  thermo.dat

The output prefix may differ from system according to fdvib.in.

See the FDVIB reference for configuration fields, physical models, output definitions, restart behavior, and diagnostics. Release history is recorded in the changelog.

FDVIB is distributed under the BSD 3-Clause License.