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About this Manual

This manual documents how to install, configure, and use TeraChem. For a high-level summary of TeraChem's capabilities, see the home page.

The remaining sections of the manual are organized as follows:

  • Introduction (this section) covers how to obtain TeraChem, how to cite it in publications, system requirements, installation, environment variables, command-line options, and licensing.
  • File Formats describes the input file syntax, accepted coordinate file formats, and how basis set files are laid out (including how to extend the library with custom basis sets and mixed-basis specifications).
  • Integrals explains how the two-electron repulsion integrals are handled — exact GPU integral-direct evaluation, density fitting (RI), and tensor hypercontraction (THC) — along with the associated precision and screening controls.
  • SCF documents Hartree-Fock and Kohn-Sham SCF, including initial guesses, FOMO-SCF, difference-density SCF, wavefunction projection, and PCM solvation.
  • Coupled Cluster covers CCSD, THC-CCSD, and EOM-CCSD.
  • Density Functional Theory documents the built-in functionals, the Libxc interface, hh-TDA, and DFT+U.
  • CASSCF describes complete active space self-consistent field calculations.
  • Optimization covers geometry optimization and transition-state search with the built-in DL-Find and geomeTRIC optimizers, conical-intersection optimization with CIOpt, and use of the external geomeTRIC Python package.
  • AIMD documents ab initio molecular dynamics, including initial-condition sampling, the nanoreactor, steered MD, and trajectory/interactive visualization.
  • QM/MM covers the internal MM-water code, the OpenMM/Amber driver, FlexiBLE, and the integral-exact direct reaction field (DRF) polarizable embedding scheme.
  • Polaritons covers calculations of molecules strongly coupled to a quantized cavity mode (Jaynes-Cummings and Pauli-Fierz Hamiltonians).
  • Exciton Model documents TeraChem's ab initio Frenkel exciton model for large multichromophore systems, including locally-excited, charge-transfer, and triplet-triplet (multiexcitonic) basis states, gradients, MD, and QM/MM embedding.
  • Properties documents charge analysis (Mulliken, Löwdin, VDD, RESP), polarizabilities, frequencies and thermochemistry, NBO6, and X-ray/UED diffraction-signal computation.
  • Interfaces documents the two server modes used to embed TeraChem in external drivers: the MPI single-point engine and TCPB (TeraChem Protocol Buffers).
  • Input File Parameters is a keyword reference for the start file. The General and Hardware/Numerical tables list parameters that apply to most jobs; the Full List page is a comprehensive keyword reference grouped by topic.

For an introduction to running TeraChem in practice, start with Getting Started.

Getting help

We are pleased to receive feedback on your experience with TeraChem. For suggestions, concerns, or bug reports, email help@petachem.com. You can also join the TeraChem User Forum, which the developers monitor frequently.