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Q-Chem Program Features

Click here for the Version 5.2 Release Log

Ground State Self-Consistent Field Methods
Hartree-Fock Methods
Density Functional Theory
Linear Scaling Methods
AOINTS Package for Two Electron Integrals
SCF Improvements
Hartree-Fock-Wigner Method
Wave Function Based Treatments of Electron Correlation
Møller-Plesset Perturbation Theory
Local MP2 Methods
Coupled Cluster Methods
Valence Space Models for Strong Correlation
Excited State Methods
Supported Calculation Types
CIS Methods
Time-Dependent DFT
Wavefunction-Based Correlated Excited State Methods
Attachment-Detachment Analysis
Properties Analysis
Automated Geometry and Transition Structure Optimization
Vibrational Spectroscopy
NMR Shielding Tensors
Analysis of Electronic Structures
Solvation Modeling
Relativistic Energy Corrections
Diagonal Adiabatic Correction
Intermolecular Interaction Analysis
Electron Transfer Analysis
Distributed Multipole Analysis
Other Analytical Tools
Basis Sets
Gaussian Basis Sets
Pseudopotential Basis Sets
Correction for Basis Set Superposition Error
Interface to CHARMM

For a complete list of features please see Q-Chem User's Guide

Graphic User Interface

  • Fully integrated graphic interface IQmol (developed by Andrew Gilbert) including molecular builder, input generator, contextual help, and visualization toolkit. For download and more information, visit www.iqmol.org

  • Integrated with Spartan

  • Support for other third-party GUI's: Avogadro, WebMO, MolDen, JMol
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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
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Density Functional Theory

  • Local Functionals and Gradient-Corrected Functionals
    • Exchange Functionals
      • Slater
      • Beckee '88 (B)
      • GGA91 (Perdew '91, PW91)
      • Gill '96
      • Gilbert and Gill '99 (GG99)
      • Handy and Cohen's OPTX (HC_OPTX)
    • Correlation Functionals
      • VWN (#5 parameterization)
      • Lee-Yang-Parr (LYP), LYP (EDF1 parameterization)
      • Perdew-Zunger '81 (PZ81)
      • Perdew '86 (P86)
      • Wigner
      • GGA91 (Perdew '91, PW91)
    • exchange-correlation functionals
      • EDF1 and Becke(EDF1)
      • PBE functionals
      • SOGGA, SOGGA11 family of GGA functionals
  • Hybrid HF-GGA Functionals
    • B3LYP, B3PW91, B3LYP5
      (using the VWN5 functional)
    • SOGGA11-X
    • User-definable hybrid functionals
  • Meta GGA Functionals
    • M06-L,M11-L
    • PK06, BR89, B94
    • TPSS
  • Hybrid Meta GGA and Hyper-GGA Functionals
    • BMK
    • MPW1B95, MPWB1K, PW6B95, PWB6K, M05, M05-2X, M06, M06-2X, M06-HF, M08, M11
    • B3tLap
    • BR89BR94hyb
    • TPSSh
    • RI-B05 for nondynamic correlation
  • Double-Hybrid Functionals
  • Long-range corrected (LRC) functionals
    • Long-range corrections from Herbert group: LRC-ωPBEPBE, LRC-ωPBEhPBE
    • Baer-Neuhauser-Livshits (BNL) functional
    • ωB97, ωB97X and ωB97X-D functionals
    • CAM-B3LYP
  • Dispersion corrections to DFT
  • Constrained DFT
    • Calculation of reactions with configuration interactions of charge-constrained states with constrained DFT
  • User-Definable Linear Combination of Functionals
  • Numerical-Grid Based Numerical Quadrature Schemes
    • The SG-0 standard grid
      • This grid is derived from a MultiExp-Lebedev-(23,170), (i.e. 23 radial points and 170 angular points per radial point). This grid was pruned whilst ensuring the error in the computed exchange energies for the atoms and a selection of small molecules was less than 10 microhartree from that computed using a very large grid.
    • The SG-1 standard grid
      • This grid is derived from a Euler-Maclaurin-Lebedev-(50,194) grid (i.e., 50 radial points, and 194 angular points per radial point).
        This grid has been found to give numerical integration errors of the order of 0.2 kcal/mol for medium-sized molecules, including particularly demanding test cases such as isomerization energies
        of alkanes.
    • Lebedev and Gauss-Legendre Angular Quadrature Schemes
      • Lebedev Spheres avaiable for up to 5294 angular points.
    • Incremental Density Function Theory
      • Improves efficiency of DFT calculations by greater amounts as convergence is reached by use of the difference denisty and Fock matrices.
  • Analytical First Derivatives for Geometry Optimizations
  • Analytical Second Derivatives for Harmonic Frequency Analysis
    • Inclusion of the first and second derivatives
      of the Becke Weighting Functions for
      greater accuracy.
  • Near-edge X-ray absorption with short-range corrected DFT
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Linear Scaling Methods

  • Fast numerical integration of exchange-correlation with mrXC (multiresolution exchange-correlation)
    • Treats the smooth and compact parts of the electron density separately
    • Highly efficient, no errors
  • Fourier Transform Coulomb Method (FTC)
  • 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 HF-exchange method (LinK)
    • Linear scaling exchange energies and gradients for cases with sparse density matrices
  • Resolution-Identity
    • Faster DFT and HF calculations with atomic resolution of the identity (ART) algorithms
  • Dual Basis
    • Fast calculation with one iteration only with the large basis basis
    • Accurate in relative energy
    • Applicable to DFT and MP2
  • Linear Scaling Grid Based Integration for Exchange-Correlation Functional Evaluation
    • Efficient computation of the exchange-correlation part of the dual basis DFT
    • Fast DFT calculation with ‘triple jumps’ between different sizes of basis set and grid and different levels of functional
  • Linear Scaling NMR Chemical Shifts
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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
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SCF Improvements

  • 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
  • Stability Analysis for SCF Wavefunctions
    • Tests for a complex solution to the SCF equations to ensure the quality of energy minima.
    • Available for restricted and unrestriced HF or DFT wavefunctions.
  • 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
  • Relaxed constraint algorithm (RCA) for converging SCF
  • 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
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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 truncations 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 standard 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
  • RI-MP2 Methods
    • Up to 10 times faster for MP2 and Local MP2
  • Dual-basis RIMP2 methods
  • Opposite-spin MP2 methods
    • Scaled opposite-spin MP2 method (SOS-MP2)
    • Modified opposite-spin MP2 method (MOS-MP2)
    • Optimized-orbitals opposite-spin MP2 method (O2)
  • Attenuated MP2 method
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Coupled-Cluster Methods

  • Significantly enhanced coupled-cluster code rewritten for better performance and multicore systems for many modules in 4.0
  • Singles and Doubles (CCSD)
    • Energies and gradients are available.
    • Frequenies available via finite differences of forces.
    • RI implementation is available (energies only)
    • XX = EE, EA, IP, SF (energies and gradients) DIP, 2SF (energies)
    • Robust treatment of radicals, bond-breaking and symmetry- breaking problems
  • Non-Iterative Corrections to the Coupled Cluster Energies
    • (T) Triples Corrections (CCSD(T)) for CC energies
    • (2) Triples and Quadruples Corrections (CCSD(2)) for CC energies
    • (dT) and (dF) corrections for CCSD, EOM-SF-CCSD, and EOM-IP-CCSD.
  • Extensive use of molecular point group and spin symmetry to improve efficiency.
  • Quadratic Coupled-Cluster Doubles
    • Improved behavior of the coupled-cluster wavefunction for such trouble cases as homolytic bond dissociation
  • QCISD, QCISD(T) and QCISD(2) energies available
  • Frozen Core Approximations, including frozen natural orbitals, available to increase treatable system size
  • Interface with EFP is avaliable for treating the effect of the environment
  • Dyson orbitals are available
  • RI/Cholesky decomposition implementation of CCSD and EOM-CCSD
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Valence Space Models for Strong Corrrelation

  • Optimized Orbital Coupled-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
    • 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), VQCCD and VOD(2) energies and gradients available
  • Perfect Quadruples and Perfect Hextuples methods
  • Coupled Cluster Valence Bond (CCVB) and related methods for multiple bond breaking
  • Extended RAS-nSF for studying excited states
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Excited State Methods

Supported Calculation Types

  • Vertical absorbtion spectrum
    • The calculation of the excited states of the molecule at the ground state geometry, as appropriate for absorption spectroscopy.
  • Excited state optimization
    • Analytic gradient available with CIS, TDDFT and EOM-CCSD
  • Excited state vibrational analysis
    • Available for UCIS, RCIS and TDDFT
  • Collinear and Non-Collinear Spin-Flip DFT
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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) and SOS-CIS(D) perturbative doubles correction available
    • Reduces the errors in CIS by a factor of two or more (to roughly that of MP2)
  • RI-CIS(D) and RI-CIS(D0) methods for faster correlated excited state calculations
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Time-Dependent DFT (TDDFT)

  • Excited state energies computed from a ground state Kohn-Sham wavefunction
  • For low-lying valence excited states, TDDFT 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
  • Spin-flip density functional threory (SFDFT)
    • Extends TDDFT to states beyond the low-lying valence states.
    • Also useful for bond-breaking processes and radical and diradical systems
  • Nuclear gradients of excited states with TDDFT
  • Direct coupling of charged states for the study of charge transfer reactions
  • Analytical excited-state Hessian in TDDFT within Tamm-Dancoff approximation
  • Improved TDDFT prediction with implementation of asymptotically corrected exchange-correlation potential (TDDFT/TDA with LB94)
  • Obtaining an excited state self-consistently with MOM (maximum overlap method)
  • Overlap analysis of the charge transfer in a excited state with TDDFT (Nick Besley, Section 6.3.2).
  • Localizing diabatic states with Boys or Edmiston-Ruedenberg localization scheme for charge or energy transfer
  • Implementation of non-collinear formulation extends SF-TDDFT to a broader set of functionals and improves its accuracy
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Wavefunction-Based Correlated Excited State Methods

  • Equation of Motion Coupled-Cluster Singles and Doubles EOM-CCSD
    • Method of computing vertical excitation energies via linear response from the ground state CC wavefunction.
  • Spin-Flip Excited State Methods
    • Improved treatment of di- and tri-radical systems.
    • Address bond-breaking problems associated with a single-determinant wavefunction.
    • Available for OD and CCSD levels of theory.
  • Excited State Property Calculations
    • Transition dipoles and getometry
  • Potential energy surface crossing minimization with EOM-CCSD
  • Correlated excited states with the perturbation-theory based, size consistent ADC scheme of second order
  • Restricted active space spin- flip method for multireference ground states and multi-electron excited states

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.
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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
  • Intrinsic Reaction Coordinates (IRC) following
    • Connect equilibrium geometries and transistion states along reaction paths.
    • Ab initio dynamics with extrapolated z-vector techniques for MP2 and/or dual-basis methods
    • Improved robustness with Version 4.0
  • Freezing and Growing String Methods for efficient automatic reaction path finding
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Vibrational Spectra

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NMR Shielding Tensors

Analysis of Electronic Structures

  • NOB 5.0, a sophisticated approach to population analysis
  • 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 computation 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
    • Complement the normal electron density in providing detailed picture of the electronic structure
  • Intracules
    • These are unique 2-electron distribution functions that provide the most detailed information about the Coulomb and exchange energies in a molecule with respect to position and momentum
    • Analytical Wigner Intracule
  • Atoms in Molecules Analysis (AIMPAC)
  • Hirshfeld population analysis
  • Localized atomic magnetic moments and correlated bond orders within DFT
  • T-Chem: Quantum transport properties via the Landauer approximation
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Solvation Modeling

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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
    • Approximately accounts for the increase of electron mass as the electron approaches the speed of light
    • Based on Dirac-Fock theory
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Diagonal Adiabatic Correction

  • Computes the Born-Oppenheimer diagonal correction in order to account for a breakdown in the adiabatic separation of nuclear and electronic motions
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Intermolecular Interaction Analysis

  • SCF with absolutely localized molecular orbitals for molecular interactions (SCF-MI)
  • Roothaan-step (RS) correction following SCF-MI
  • Energy decomposition analysis (EDA)
  • Complementary occupied-virtual pair (COVP) analysis for charge transfer
  • Automated basis-set superposition error (BSSE) calculation
  • Symmetry-adapted perturbation theory for intermolecular interaction energy decomposition
  • XPol monomer-based SCF calculations of many-body polarization effects
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Other Analytical tools

  • Analysis of metal oxidation states via localized orbital bonding analysis
  • Visualization of noncovalent bonding using Johnson and Yang’s algorithm
  • ESP on a grid for transition density
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Basis Sets

Gaussian Basis Sets

  • strong>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 Ahlrichs double and triple zeta basis sets are also available
  • G3Large basis set for transition metals
  • User-specified basis sets supported
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Pseudopotential Basis Sets

  • These sets incorporate relativistic effects
  • PRISM now supports fully analytical treatment of integrals 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
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Correction for Basis Set Superposition Error (BSSE)

  • Places basis functions on ghost atoms to correct the overestimation of binding energies.
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Interface to CHARMM

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Support for Modern Computing Platforms

  • New OpenMP capabilities for SCF/DFT, MP2, integral transformation and coupled cluster theory ion modern multi-core systems
  • Accelerating RI-MP2 calculation with GPU (graphic processing unit)
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More details on the new features of Q-Chem 4 can be found in the Version 4 User's Guide.