Molecular modelling,drawing, molecular mechanics, Semi-empirical calculations, structure display

All included as standard

  1. HSC Thermochemical Database
  2. Water Steam/Fluid Database
  3. Heat Conduction Database
  4. Heat Convection Database
  5. Surface Radiation Database
  6. Gas Radiation Calculator
  7. Particle Radiation Calculator
  8. Elements Database
  9. Measure Units Database
  10. Minerals Database
  11. Aqueous Solution Density Database
  12. The Pitzer parameter Database
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Version 9 Modules
All modules included as standard

  1. Sim - Process simulation
  2. LCA Evaluation
  3. Mass Balance
  4. Reaction Equations
  5. Heat and Material Balances
  6. Heat Loss Calculator
  7. Equilibrium Calculations
  8. Exergy Balance
  9. Eh-pH Diagrams - Pourbaix
  10. H, S, Cp and Ellingham Diagrams
  11. Tpp Diagram-Stability diagrams
  12. Lpp Diagrams-Stability diagrams
  13. Water - Steam tables, etc.
  14. H, S, Cp Estimates
  15. Benson Estimation
  16. Species Converter
  17. Periodic Chart-Elements
  18. Measure Units
  19. HSC AddIn Functions
  20. Aqua
  21. Geo-Mineralogical calculations
  22. Map-GPS material stock
  23. Fit-Numerical Data fit
  24. Data-Statistical analysis

All included as standard

  1. HSC Thermochemical Database
  2. Water Steam/Fluid Database
  3. Heat Conduction Database
  4. Heat Convection Database
  5. Surface Radiation Database
  6. Gas Radiation Calculator
  7. Particle Radiation Calculator
  8. Elements Database
  9. Measure Units Database
  10. Minerals Database
  11. Aqueous Solution Density Database
  12. The Pitzer parameter Database
US Flag
(866) 571-1976

UK Flag
01737 822144

sales and support
  Q-Chem 2.0TM

Datasheet pdf 1.44Mb (full user guide)
OS Linux, SGI, DEC Alpha,compaq MPI, HP-UX systems, Sun Solaris
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Q-Chem 2.0 is the newest version of our modern ab initio of our electronic structure program package, capable of performing first principles calculations on the ground and excited states of molecules.

New in Q-Chem 2.1

  • Algorithms for large-molecule
  • DFT calculations
  • ECPs for transition metals
  • Analytic Frequency for DFT
  • Local MP2
  • High level electron correlational methods
  • DFT for excited states
  • Langevin dipoles solvation model .


  Ground State Self-Consistent Field Methods

Hartree-Fock Theory
  • Restricted, Unrestricted, and Restricted Open-Shell Formulations

  • Analytical First Derivatives for Geometry Optimizations

  • Analytical Second Derivatives for Harmonic Frequency Analysis

Density Functional Theory

  • Local Functionals and Gradient-Corrected Functionals

    • Exchange Functionals
      • Slater
      • Becke '88 (B)
      • GGA91 (Perdew '91, PW91)
      • Gill '96
      • Gilbert and Gill '99 (GG99)
    • Correlation Functionals
      • VWN (#5 parameterization)
      • Lee-Yang-Parr (LYP), LYP(EDF1 parameterization)
      • Perdew-Zunger '81 (PZ81)
      • Perdew '86 (P86)
      • Wigner
      • GGA91 (Perdew '91, PW91)
    • EDF1 and Becke(EDF1) exchange-correlation functionals
    • User-definable exchange-correlation functionals

  • Hybrid HF-DFT Functionals

    • B3LYP, B3PW91, B3LYP5 (using the VWN5 functional)
    • User-definable hybrid functionals

  • Numerical-Grid Based Numerical Quadrature Schemes
    • The SG-1 standard grid
    • Lebedev and Gauss-Legendre Angular Quadrature Schemes

  • Analytical First Derivatives for Geometry Optimizations

  • Analytical Second Derivatives for Harmonic Frequency Analysis

Linear Scaling Methods

  • Continuous Fast Multipole Method (CFMM)
    • Fastest ab initio implementation of multipole-based methods
    • Linear-cost calculation of electronic Coulomb interactions
    • Finds exact Coulomb energy; no approximations are made
    • Efficiently calculates energy and gradient

  • Linear-Scaling K method
    • Linear scaling exchange energies and gradients for cases with sparse density matrices

  • Linear Scaling Grid Based Integration for Exchange-Correlation Functional Evaluation
Q-Chem's AOINTS Package for Two Electron Integrals

  • Incorporates the latest advances in high performance integrals technology

    • The most efficient method available for evaluation of two-electron Gaussian integrals
    • Algorithms choose the optimum method for each integral given the angular momentum and degree of contraction
    • Analytical solution of integrals over pseudopotential operators

  • J Matrix engine
    • Direct computation of Coulomb matrix elements approximately 10 times faster than explicit integral evaluation.
SCF Improvement Features

  • Automated optimal hybrid of in-core and direct SCF methods

  • Direct Inversion in the Iterative Subspace (DIIS)
    • Drastically reduces the number of iterations necessary to converge the SCF

  • Initial Guessing Schemes
    • Improves the initial starting point for the SCF procedure
    • Superposing spherical averaged atomic densities (SAD)
    • Generalized Wolfsberg-Helmholtz (GWH)
    • Projection from smaller basis sets
    • Core Hamiltonian Guessing

  • Maximum Overlap Method (MOM)
    • Prevents oscillation of the occupations at each iteration that can hinder convergence
    • Scales cubic with the number of orbitals

  • Direct Minimization of the Fock Matrix
    • Follows the energy gradients to minimize the SCF energy providing a useful alternative to DIIS

  • Intermediate molecular-optimized minimal basis of polarized atomic orbitals (PAOs)
    • Set of orbitals defined by a atom-blocked linear transformation from the fixed atomic orbital basis
    • Potential computational advantages for local MP2 compuations
    • Analytical gradients and second-order corrections to the energy available
Wave Function Based Treatments of Electron Correlation

Møller-Plesset Theory

  • Second-Order Møller-Plesset Theory (MP2)
    • Restricted, Unrestricted, and Restriced Open-Shell Formulations Available
    • Energy via direct and semi-direct methods
    • Analytical gradient via efficient semi-direct method available for restricted and unrestricted formalisms
    • Proper treatment of frozen orbitals in analytical gradient
  • Energy via MP3, MP4 and MP4SDQ methods also available

Local MP2 Methods
  • Drastically reduces cost through physically motivated tructions of the full MP2 energy expression

  • Reduces the scaling of the computation with molecular size
    • Capable of performing MP2 computations on molecules roughly twice the size as capable with MP2 without significant loss of accuracy!

  • Utilizes extrapolated PAO's (EPAO's) for local correlation

  • Available methods are the TRIM (triatomics in molecules) and DIM (diatomics in molecules) techniques
    • Yields contiuous potential energy surfaces
    • TRIM recovers around 99.7% of the full MP2 energy
    • DIM recovers around 95% of the full MP2 energy


Coupled-Cluster Methods
  • CCD, CCSD, and CCSD(T), and CCSD(2)
    • Energies available

  • QCISD, QCISD(T) and QCISD(2) energies available
    • Energies available


Optimized Orbital Coupled-Cluster Methods
  • Optimized Orbital Couple-Cluster Doubles (OD)
    • Helpful in avoiding artifactual symmetry breaking problems
    • The mean-field reference orbitals are optimized to minimize the total energy
    • Alternative approach to Brueckner coupled-cluster
    • OD, OD(T), and OD(2) energies and gradients available

  • Valence Optimized Orbital Coupled-Cluster Doubles (VOD)
    • Coupled-cluster approximation of the traditional CASSCF method.
    • A truncated OD wave function is utilized within a valence active space
    • Requires far less disk space and scales better with system size than CASSCF so that larger systems can be treated
    • VOD, VOD(T), and VOD(2) energies and gradients available
Excited State Methods

CIS Methods

  • Excited states are computed starting from a Hartree-Fock wavefunction
    • Provides qualitatively correct descriptions of single-electron excited states
    • Geometries and frequencies comparable to ground-state Hartree-Fock results

  • Efficient, direct algorithm for computing closed- and open- shell energies, analytical gradients and second derivatives

  • CIS (XCIS) Method available
    • Comparible results to the closed-shell CIS method for doublet and quartet states

  • CIS(D) perturbative doubles correction available
    • Reduces the errors in CIS by a factor of two or more (to roughly that of MP2)

Time-Dependent DFT (TD-DFT)

  • Excited state energies computed from a ground state Kohn-Sham wavefunction

  • For low-lying valence excited states, TD-DFT provides a marked improvement over CIS, at about the same cost

  • Provides an implicit representation of correlation effects in excited states

  • Provides marked improvement over CIS for low-lying valence excited states of radicals


Coupled-Cluster Based Excited State Methods

  • OOD method
    • Essentially identical numerical performance to CCSD excited state energies
    • Higher accuracy than TD-DFT, but more computationally expensive

  • Equation of Motion VOOD method
    • Similar to EOM-CCSD cast into the VOOD scheme

Attachment-Detachment Analysis for Excited States

  • A unique tool for visualizing electronic transtions
    • Utilizes the difference density matrix between the ground exctied state to create a one-electron picture of electronic transitions
    • Useful in classifying the character electronic transistion as valence, Rydberg, mixed, or charge-transfer.
Property Analysis

Automated Geometry and Transition Structure Optimization

  • Uses Dr. Jon Baker's OPTIMIZE package
    • Utilizes redundant internal coordinates to ensure rapid convergence even without an initial force constant matrix

  • Geometry Optimization with General Constraints
    • Can impose bond angle, dihedral angle (torsion) or out-of-plane bend constraints
    • Freezes atoms in Cartesian coordinates
    • Desired constraints do not need to be imposed in starting structure

  • Optimizes in Cartesian, Z-Matrix or delocalized internal coordinates

  • Eigenvector Following (EF) algorithm for minima and transition states

  • GDIIS algorithm for minima
    • Greatly speeds up convergence to an equilibrium geometry

Vibrational Spectra

  • Automated with both analytical and numerical second-derivatives

  • Infrared and Raman intensities

  • Outputs standard statistical thermodynamic information


Natural Bond Orbital Analysis

  • A sophistocated approach to population analysis

  • Q-Chem provided with NBO version 4.0

Stewart Atoms

  • Recovers the atomic identity from a molecular density
    • Provides a simplified representation of the electronic density

  • Q-Chem utilizes the resolution of the identity (RI) for computaion of these values.

Momentum Densities

  • Property that shows what momentum an electron is most likely to possess

  • Useful in comparison to Compton scattering experiment results

  • Compliment the normal electron density in providing detailed picture of the electronic structure


  • Q-Chem can compute these functions that provide information can provide information about the Coulomb and exchange energies in a molecule with respect to position and momentum

Solvation Modelling

  • Include solvation effects in ab-initio computations through the use of two models
    • The simple Onsager reaction field model
    • The Langevin dipoles model
      • Continuum model that realistically treats solvation effects by adding a layer of dipoles around the Van der Waals surface of the solute

Relativistic Energy Corrections

  • Additive correction to the Hartree-Fock energy is computed atomatically everytime a frequency calculation is requested
    • Needed for an accurate description of heavy-atoms
    • Approximately accounts for the increase of electron mass as the electron approaches the speed of light
    • Based on Dirac-Fock theory

Diagonal Adiabatic Correction

  • Computes the Born-Oppenheimer diagonal correction in order account a breakdown in the seperation of nuclear and electronic motion
Basis Sets

Gaussian Basis Sets

  • Standard Pople Basis Sets
    • 3-21G (H-Cs), 4-31G (H-Cl), 6-31G (H-Kr), and 6-311G (H-Kr)
    • polarization and diffuse function extensions

  • Dunning's systematic sequence of correlation consistent basis sets
    • Obtained from the Pacific Northwest Basis Set Database
    • cc-pVDZ, cc-pVTZ, cc-pVQZ, cc-pV5Z for H-Ar
    • augmented versions of these sets for H-Ar
    • core-valence effects included through the cc-pCVXZ basis set for B-Ne
    • DZ and TZ basis sets also available

    The modern Ahlrich's double and triple zeta basis sets are also available
  • User-specified basis sets supported

Pseudopotential Basis Sets

  • These sets incorporate relativistic effects

  • PRISM now supports fully analytical treatment of intergrals over pseudopotential operators

  • Standard pseudopotential sets obtained from the Pacific Northwest Basis Set Database

  • Available sets are:
    • The Hay-Wadt minimal basis
    • The Hay-Wadt valence double zeta basis
    • lanl2dz (mimic of Gaussian's lanl2dz)
    • Stevens-Bausch-Krauss-Jaisen-Cundari-21G
    • CRENBL-Christiansen et al. shape consistent large orbital,small core
    • CRENBS-Christiansen et al. shape consistent small basis large core
    • Stuggart relativistic large core
    • Stuggart relativistic small core

  • User-defined pseudopotential basis sets supported