QChem Program Features
Click here for the Version 5.1 Release Log
 Ground State SelfConsistent Field Methods
 HartreeFock Methods
 Density Functional Theory
 Linear Scaling Methods
 AOINTS Package for Two Electron Integrals
 SCF Improvements
 HartreeFockWigner Method
 Wave Function Based Treatments of Electron Correlation
 MøllerPlesset Perturbation Theory
 Local MP2 Methods
 Coupled Cluster Methods
 Valence Space Models for Strong Correlation
 Excited State Methods
 Supported Calculation Types
 CIS Methods
 TimeDependent DFT
 WavefunctionBased Correlated Excited State Methods
 AttachmentDetachment 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
 QM/MM
 Interface to CHARMM
 ONIOM
For a complete list of features please see QChem 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 thirdparty GUI's: Avogadro, WebMO, MolDen, JMol
Back to Top
Ground State SelfConsistent Field Methods
HartreeFock Theory
 Restricted, Unrestricted, and Restricted OpenShell Formulations
 Analytical First Derivatives for Geometry Optimizations
 Analytical Second Derivatives for Harmonic Frequency Analysis
Back to Top
Density Functional Theory
 Local
Functionals and GradientCorrected 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)
 LeeYangParr (LYP), LYP (EDF1 parameterization)
 PerdewZunger '81 (PZ81)
 Perdew '86 (P86)
 Wigner
 GGA91 (Perdew '91, PW91)
 exchangecorrelation functionals
 EDF1 and Becke(EDF1)
 PBE functionals
 SOGGA, SOGGA11 family of GGA functionals
 Exchange Functionals
 Hybrid
HFGGA Functionals
 B3LYP, B3PW91, B3LYP5
(using the VWN5 functional)  SOGGA11X
 Userdefinable hybrid functionals
 B3LYP, B3PW91, B3LYP5
 Meta GGA Functionals
 M06L,M11L
 PK06, BR89, B94
 TPSS
 Hybrid Meta GGA and HyperGGA Functionals
 BMK
 MPW1B95, MPWB1K, PW6B95, PWB6K, M05, M052X, M06, M062X, M06HF, M08, M11
 B3tLap
 BR89BR94hyb
 TPSSh
 RIB05 for nondynamic correlation
 DoubleHybrid Functionals
 Longrange corrected (LRC) functionals
 Longrange corrections from Herbert group: LRCωPBEPBE, LRCωPBEhPBE
 BaerNeuhauserLivshits (BNL) functional
 ωB97, ωB97X and ωB97XD functionals
 CAMB3LYP
 Dispersion corrections to DFT
 Becke and Johnson’s XDM model
 vdwDF04 of Langreth, Lundqvist and coworkers’
 VV09
 D2 and D3 of Grimme's
 B97D
 ωB97XD
 Constrained DFT
 Calculation of reactions with configuration interactions of chargeconstrained states with constrained DFT
 UserDefinable Linear Combination of Functionals
 NumericalGrid Based Numerical Quadrature Schemes
 The SG0 standard grid
 This grid is derived from a MultiExpLebedev(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 SG1 standard
grid
 This grid is derived from
a EulerMaclaurinLebedev(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 mediumsized molecules, including particularly demanding test cases such as isomerization energies
of alkanes.
 This grid is derived from
a EulerMaclaurinLebedev(50,194)
grid (i.e., 50 radial points,
and 194 angular points per radial point).
 Lebedev and GaussLegendre
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.  Nearedge Xray absorption with shortrange corrected DFT
Back to Top
Linear Scaling Methods
 Fast numerical integration of exchangecorrelation with mrXC (multiresolution exchangecorrelation)
 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 multipolebased methods
 Linearcost calculation of electronic Coulomb interactions
 Finds exact Coulomb energy; no approximations are made
 Efficiently calculates energy and gradient
 LinearScaling HFexchange method (LinK)
 Linear scaling exchange energies and gradients for cases with sparse density matrices
 ResolutionIdentity
 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 ExchangeCorrelation Functional Evaluation
 Efficient computation of the exchangecorrelation 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
Back to Top
QChem's AOINTS Package for Two Electron Integrals
 Incorporates the latest advances in high performance integrals technology
 COLD PRISM
 The most efficient method available for evaluation of twoelectron 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
Back to Top
SCF Improvements
 Automated optimal hybrid of incore 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 WolfsbergHelmholtz (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 molecularoptimized minimal basis of polarized atomic orbitals PAOs)
 Set of orbitals defined by a atomblocked linear transformation from the fixed atomic orbital basis
 Potential computational advantages for local MP2 compuations
 Analytical gradients and secondorder corrections to the energy available
Back to Top
Wave Function Based Treatments of Electron Correlation
MøllerPlesset Theory
 SecondOrder MøllerPlesset
Theory (MP2)
 Restricted, Unrestricted, and Restriced OpenShell Formulations Available
 Energy via direct and semidirect methods
 Analytical gradient via efficient semidirect 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

RIMP2 Methods
 Up to 10 times faster for MP2 and Local MP2
 Dualbasis RIMP2 methods
 Oppositespin MP2 methods
 Scaled oppositespin MP2 method (SOSMP2)
 Modified oppositespin MP2 method (MOSMP2)
 Optimizedorbitals oppositespin MP2 method (O2)
 Attenuated MP2 method
Back to Top
CoupledCluster Methods
 Significantly enhanced coupledcluster 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)
 EOMXXCCSD
 XX = EE, EA, IP, SF (energies and gradients) DIP, 2SF (energies)
 Robust treatment of radicals, bondbreaking and symmetry breaking problems
 NonIterative
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, EOMSFCCSD, and EOMIPCCSD.
 Extensive use of molecular point group and spin symmetry to improve efficiency.
 Quadratic CoupledCluster Doubles
 Improved behavior of the coupledcluster 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 EOMCCSD
Back to Top
Valence Space Models for Strong Corrrelation
 Optimized Orbital CoupledCluster
Doubles (OD)
 Helpful in avoiding artifactual
symmetry
breaking problems  The meanfield reference orbitals are optimized to minimize the total energy
 Alternative
approach to Brueckner
coupledcluster  OD, OD(T), and OD(2) energies and
gradients available
 Helpful in avoiding artifactual
symmetry
 Valence Optimized Orbital
CoupledCluster
Doubles (VOD) Coupledcluster 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 RASnSF for studying excited states
Back to Top
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 EOMCCSD
 Excited state vibrational
analysis
 Available for UCIS, RCIS and TDDFT
 Collinear and NonCollinear SpinFlip DFT
Back to Top
CIS Methods
 Excited states are computed
starting from a
HartreeFock wavefunction Provides qualitatively correct descriptions of singleelectron excited states
 Geometries and frequencies comparable to groundstate HartreeFock results
 Efficient, direct algorithm for computing closed and open shell energies, analytical gradients and second derivatives
 CIS (XCIS) Method
available
 Comparible results to the closedshell CIS method for doublet and quartet states
 CIS(D) and SOSCIS(D) perturbative doubles
correction available
 Reduces the errors in CIS by a factor of two or more (to roughly that of MP2)
 RICIS(D) and RICIS(D0) methods for faster correlated excited state calculations
Back to Top
TimeDependent DFT (TDDFT)
 Excited state energies computed from a ground state KohnSham wavefunction
 For lowlying 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 lowlying valence excited states of radicals
 Spinflip density functional threory (SFDFT)
 Extends TDDFT to states beyond the lowlying valence states.
 Also useful for bondbreaking 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 excitedstate Hessian in TDDFT within TammDancoff approximation
 Improved TDDFT prediction with implementation of asymptotically corrected exchangecorrelation potential (TDDFT/TDA with LB94)
 Obtaining an excited state selfconsistently 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 EdmistonRuedenberg localization scheme for charge or energy transfer
 Implementation of noncollinear formulation extends SFTDDFT to a broader set of functionals and improves its accuracy
Back to Top
WavefunctionBased Correlated Excited State Methods
 Equation of Motion CoupledCluster
Singles and Doubles EOMCCSD
 Method of computing vertical excitation energies via linear response from the ground state CC wavefunction.
 SpinFlip Excited State Methods
 Improved treatment of di and triradical systems.
 Address bondbreaking problems associated with a singledeterminant wavefunction.
 Available for OD and CCSD levels of theory.
 Excited State Property Calculations
 Transition dipoles and getometry
 Potential energy surface crossing minimization with EOMCCSD
 Correlated excited states with the perturbationtheory based, size consistent ADC scheme of second order
 Restricted active space spin flip method for multireference ground states and multielectron excited states
AttachmentDetachment Analysis for Excited States
 A
unique tool
for visualizing
electronic transtions
 Utilizes the difference density matrix between the ground exctied state to create a oneelectron picture of electronic transitions
 Useful in classifying the character electronic transistion as valence, Rydberg, mixed, or chargetransfer.
Back to Top
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 outofplane bend constraints Freezes atoms in Cartesian coordinates
 Desired constraints do not need to be imposed in starting structure
 Optimizes in Cartesian, ZMatrix 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 zvector techniques for MP2 and/or dualbasis methods
 Improved robustness with Version 4.0
 Freezing and Growing String Methods for efficient automatic reaction path finding
Back to Top
Vibrational Spectra
 Automated with both analytical and numerical secondderivatives
 Infrared and Raman intensities
 Outputs standard statistical thermodynamic information
 Isotropic subsitution available for comparison with experiment
 Anharmonic correction
 Partial hessian analysis
 Exact, quantum mechanical treatment of nuclear motions at equilibrium with path integral methods.
 Calculation of local vibrational modes of interest with partial Hessian vibrational analysis.
 Quasiclassical ab initio molecular dynamics.
Back to Top
NMR Shielding Tensors
 NMR chemical shifts provides a reliable comparison between the experimentally measured NMR signals and structural properties.
 First and only linearscaling NMR calculation with hundreds of atoms
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
 QChem 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 2electron 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)
 QChem can now produce output suitable for use by the AIMPAC program, which is a freely available program that performs AIM analysis.
 AIMPAC is available at www.chemistry.mcmaster.ca/aimpac/imagemap/imagemap.htm
 Hirshfeld population analysis
 Localized atomic magnetic moments and correlated bond orders within DFT
 TChem: Quantum transport properties via the Landauer approximation
Back to Top
Solvation Modeling
 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
 SS(V)PE: a new dielectric continuum model
 SM8 solvation model
 Smooth solvation energy surface with switching/Gaussian polarizable continuum medium PCM) solvation models for QM and QM/MM calculations.
 The original COSMO solvation model by Klamt and Schüürmann with DFT energy and gradient.
Back to Top
Relativistic Energy Corrections
 Additive correction to the
HartreeFock energy is computed atomatically
everytime a frequency calculation is requested
 Needed for an accurate
description of
heavyatoms  Approximately accounts for the increase of electron mass as the electron approaches the speed of light
 Based on DiracFock theory
 Needed for an accurate
description of
Back to Top
Diagonal Adiabatic Correction
 Computes the BornOppenheimer diagonal correction in order to account for a breakdown in the adiabatic separation of nuclear and electronic motions
Back to Top
Intermolecular Interaction Analysis
 SCF with absolutely localized molecular orbitals for molecular interactions (SCFMI)
 Roothaanstep (RS) correction following SCFMI
 Energy decomposition analysis (EDA)
 Complementary occupiedvirtual pair (COVP) analysis for charge transfer
 Automated basisset superposition error (BSSE) calculation
 Symmetryadapted perturbation theory for intermolecular interaction energy decomposition
 XPol monomerbased SCF calculations of manybody polarization effects
Back to Top
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
Back to Top
Basis Sets
Gaussian Basis Sets
 strong>Standard
Pople Basis Sets
 321G (HCs), 431G (HCl), 631G (HKr), and 6311G (HKr)
 Polarization and diffuse function extensions

Dunning's systematic sequence of correlation
consistent basis sets
 Obtained from the Pacific Northwest Basis Set Database ccpVDZ, ccpVTZ, ccpVQZ, ccpV5Z for HAr
 Augmented versions of these sets for HAr
 Corevalence effects included through the ccpCVXZ basis set for BNe
 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
 Userspecified basis sets supported
Back to Top
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 HayWadt minimal basis
 The HayWadt valence double zeta basis
 lanl2dz (mimic of Gaussian's lanl2dz)
 StevensBauschKraussJaisenCundari21G
 CRENBLChristiansen et al. shape consistent large orbital, small core
 CRENBSChristiansen et al. shape consistent small basis, large core
 Stuggart relativistic large core
 Stuggart relativistic small core
 Userdefined pseudopotential basis sets supported
Back to Top
Correction for Basis Set Superposition Error (BSSE)
 Places basis functions on ghost atoms to correct the overestimation of binding energies.
Back to Top
QM/MM
Interface to CHARMM
 YinYang Atom model without linked atoms
 ONIOM model implemented
 The QM/MM interface between QChem and CHARMM is distributed with the standard release version of CHARMM. More information about CHARMM can be obtained by following the links listed below.
 Release schedule: http://www.charmm.org/package/logindex.shtml
 License: http://www.charmm.org/info/license.shtml
 Singlepoint energy, geometry optimization, and hessian analysis with QM/MM
 For more information about using the QChem/CHARMM QM/MM interface please refer to the following
 Interfacing QChem and CHARMM to Perform QM/MM Reaction Path Calculations. H. Lee Woodcock III, Milan Hodoscek, Andrew T.B. Gilbert, Peter M.W. Gill, Henry F. Schaefer III, and Bernard R. Brooks. J. Comp. Chem. 28, 1485, 2007. http://www.charmm.org/document/Charmm/cXXbY/qchem.html (cXXbY = current release version). For additional information please contact Dr. H. Lee Woodcock (hlwood@nih.gov)
 Effective fragment orbital (EFP) approach for accurate and fast energy computation for large systems including polarizable explicit solvation for ground and excited states using DFT/TDDFT, CCSD/EOMCCSD, as well as CIS and CIS(D); library of effective fragments for common solvents; energy gradient for EFPEFP systems
 fEFP method extending EFP to macromolecules
Back to Top
Support for Modern Computing Platforms
 New OpenMP capabilities for SCF/DFT, MP2, integral transformation and coupled cluster theory ion modern multicore systems
 Accelerating RIMP2 calculation with GPU (graphic processing unit)
Back to Top
More details on the new features of QChem 4 can be found in the Version 4 User's Guide.
© 2018 QChem, Inc., All rights reserved.
Send us your feedback regarding website content, functionality or submit an enhancement request.
Send us your feedback regarding website content, functionality or submit an enhancement request.