Chemical Reactions


Q-Chem provides a suite of tools for calculating and analyzing potential energy surfaces to assist in the understanding of chemical reactions.



Geometry Optimization


  • Optimization in automatically generated internal coordinates
  • Constrained optimization
  • L-BFGS algorithm for large QM/MM optimizations
  • Hessian-free methods for stationary point characterization



Potential Energy Surface Scans


  • Both relaxed and unrelaxed PES scans
  • Support for scanning over one or two independent geometric variables



Transition Structure Search


  • All geometry optimization features are available for transition structure optimization
  • The Freezing String Method (FSM) automates the search for candidate transition structures
  • Hessian-free methods automatically launched from FSM
  • Improved dimer method



Intrinsic Reaction Coordinate


  • Automatically determines which minima are connected to a given transition structure
  • Reaction paths can be followed in either Z-matrix, Cartesian or mass-weighted Cartesian coordinates



Minimum Energy Crossing Points

Transition structure search