Q-Chem Program Features
The Q-Chem program exploits the latest developments in computer science, having adopted an Object Oriented approach to program design, which has been made possible by constructing a completely new program from the ground up. This decision is already proving invaluable in allowing developers to rapidly implement new methodologies with ease and reduce program code redundancy. The result is a highly efficient program with a flexible development base, making Q-Chem, Inc. the company of choice for quantum chemistry software.
Theoretical Methods | Properties Analysis | Basis Sets
Q-Chem incorporates the features highlighted here, among others:Hartree-Fock Theory
Local and Gradient-Corrected Density Functional Theory
- Automated optimal hybrid of in-core and direct SCF methods
- Linear-cost exchange algorithm for large molecules (ONX)
- Linear-cost Coulomb Algorithms (QCTC, CFMM)
- Linear-cost Coulomb Attenuated Schrodinger Equation (CASE)
Hybrid HF-DFT Methods
- Slater, Becke, GGA91 and Gill '96 exchange functionals
- VWN (#5), PZ81, Wigner, Perdew '86, LYP and GGA91 correlation functionals
- Linear-cost XC algorithm (CPU and memory) for large molecules
- EDF1
- User-definable exchange-correlation functionals
Continuous Fast Multipole Method (CFMM)
- B3LYP
- B3P
- User-definable hybrids
MP2 Perturbation Theory
- 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
CIS, XCIS and CIS(D) Methods for Excited States
- Energy via direct and semi-direct methods
- Analytical gradient via efficient semi-direct method
- Proper treatment of frozen orbitals in analytical gradient
- Excited states treated via the corresponding CIS(D) method
Q-Chem's AOINTS package for Two-Electron Integrals
- Restricted, unrestricted and restricted open shell CIS supported
- Analytical gradients and Hessians available for restricted and unrestricted CIS
- CIS implementations are direct methods designed for large molecules
- CIS(D) treats electron correlation effects on electronic transitions
- Efficient direct and semi-direct implementation of CIS(D) makes the cost of this method per state similar to MP2
- Incorporates the latest advances in high performance integrals technology
- COLD PRISM
- J Matrix engine
Automated Geometry and Transition Structure Optimization
Vibrational Spectra
- Uses Jon Baker's OPTIMIZE package
- 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
Electronic Excitation Spectra
- Infrared and Raman intensities
- Outputs standard statistical thermodynamic information
Molecular Orbital and Density Plotting
- Excitation energies may be calculated at the CIS, XCIS and CIS(D) levels
- Visualization via attachment-detachment analysis at the CIS level of theory
Natural Bond Orbital Analysis
- Seamless integration with HyperChem plotting features
Attachment-Detachment Analysis for Excited States
- Q-Chem provided with NBO version 4.0
- A unique new tool for visualizing electronic transitions
- Large number of standard basis sets built-in
- Pople
- Dunning
- Ahlrichs
- Simple format for user-defined basis sets
- Ability to define different basis sets for different atoms
- Basis set exponents and contraction coefficients printable in input format for easy modification
- Basis sets obtained from PNL Basis Set Library
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| Page last modified Sunday, 04-Apr-1999 19:59:34 EDT |