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Q-Chem incorporates the features highlighted here, among others:
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|
Properties Analysis |
| Automated Geometry and
Transition Structure Optimization |
| Optimizes in Cartesian, Z-Matrix or
delocalized internal coordinates |
| Eigenvector Following (EF) algorithm for
minima and transition states |
| GDIIS algorithm for minima |
| Can impose bond angle, dihedral angle
(torsion) or out-of-plane bend constraints |
| Freezes atoms in Cartesian coordinates
|
| Desired constraints need not be satisfied in
the starting structure |
| Geometry optimization in the presence of
fixed point charges |
| Vibrational Spectra |
| Electronic Excitation Spectra
|
| Excitation energies may be calculated at the
CIS, XCIS and CIS(D) levels |
| Visualization via attachment-detachment
analysis at the CIS level of theory |
| Electrostatic Potentials
|
| Molecular Orbital and Density Plotting
|
| Seamless integration with HyperChem and
UniChem plotting features |
| Natural Bond Orbital Analysis
|
| Attachment-Detachment Analysis for
Excited States |
| A unique new tool for visualizing electronic
transitions |
| Automated visualization available within
HyperChem and UniChem interfaces |
|
Theoretical Methods |
| Hartree-Fock Theory
|
| Automated optimal blend of in-core and
direct SCF methods |
| Linear-cost exchange algorithms for large
molecules (QCTC, ONX) |
| Local and Gradient-Corrected Density
Functional Theory |
| Slater, Becke and GGA91 exchange
functionals |
| VWN, PZ81, Wigner, Perdew '86, LYP and
GGA91 correlation functionals |
| Linear-cost XC algorithm for large
molecules |
| Hybrid HF-DFT Methods
|
| B3LYP |
| B3P |
| User-definable hybrids |
| Continuous Fast Multipole
Method (CFMM) |
| Linear-cost calculation of Coulomb
interactions |
| Finds exact Coulomb energy; no
approximations are made |
| MP2 Perturbation Theory
|
| Energy via direct and semidirect
methods |
| Analytical gradient via efficient semidirect
methods |
| Proper treatment of frozen orbitals in
analytical gradient |
| Excited states treated via the corresponding
CIS(D) method |
| CIS, XCIS and CIS(D) Methods for
Excited States |
| Restricted, unrestricted and restricted open
shell CIS supported |
Energies and gradients available for
restricted and unrestricted CIS with energies
available for all
other methods |
| CIS implementations are direct methods designed
for large molecules |
| CIS(D) treats electron correlation effects on
electronic transitions |
Efficient direct and semidirect implementation
of CIS(D) makes the cost of this
method per state similar to MP2
|
| COLD PRISM for Two-Electron
Integrals |
| Incorporates the latest advances in
integrals methodology |
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