View source for Q-Chem

{{Infobox software
| logo = Q-Chem logo.png
| name = 
| developer = Q-Chem Inc., Q-Chem developer community
| latest release version = 6.2.2
| latest release date = {{Start date and age|2024|11|21|df=yes}}
| programming language = [[Fortran]], [[C (programming language)|C]], [[C++]]
| operating_system = [[Linux]], [[FreeBSD]], [[Unix]] and [[Unix-like|like]] operating systems, [[Microsoft Windows]], [[Mac OS X]]
| genre = [[Ab initio quantum chemistry methods|Ab initio quantum chemistry]], [[Density functional theory]], [[QM/MM]], [[Molecular dynamics|AIMD]], [[Computational chemistry]]
| license = Commercial, academic
| website = {{URL|www.q-chem.com}}
}}

'''Q-Chem''' is a general-purpose electronic structure package<ref name='QC2.0'>{{cite journal|last1=Kong|first1=Jing|last2=White|first2=Christopher A.|last3=Krylov|first3=Anna I.|last4=Sherrill|first4=David|last5=Adamson|first5=Ross D.|last6=Furlani|first6=Thomas R.|last7=Lee|first7=Michael S.|last8=Lee|first8=Aaron M.|last9=Gwaltney|first9=Steven R.|title=Q-Chem 2.0: a high-performance ab initio electronic structure program package|journal=Journal of Computational Chemistry|volume=21|page=1532|year=2000|doi=10.1002/1096-987X(200012)21:16<1532::AID-JCC10>3.0.CO;2-W|issue=16|citeseerx=10.1.1.318.9340|s2cid=62253160 }}</ref><ref name='QC3.0'>{{cite journal | title = Advances in methods and algorithms in a modern quantum chemistry program package | journal = Physical Chemistry Chemical Physics | year = 2006 | pages = 3172–3191 | volume = 8 |bibcode = 2006PCCP....8.3172S |doi = 10.1039/b517914a | issue = 27 | pmid = 16902710 | last1 = Shao | first1 = Y. | last2 = Molnar | first2 = L. F. | last3 = Jung | first3 = Y. | last4 = Kussmann | first4 = J. | last5 = Ochsenfeld | first5 = C. | last6 = Brown | first6 = S. T. | last7 = Gilbert | first7 = A. T. | last8 = Slipchenko | first8 = L. V. | last9 = Levchenko | first9 = S. V. | last10 = O'Neill | first10 = D. P. | last11 = Distasio Jr | first11 = R. A. | last12 = Lochan | first12 = R. C. | last13 = Wang | first13 = T. | last14 = Beran | first14 = G. J. | last15 = Besley | first15 = N. A. | last16 = Herbert | first16 = J. M. | last17 = Lin | first17 = C. Y. | last18 = Van Voorhis | first18 = T. | last19 = Chien | first19 = S. H. | last20 = Sodt | first20 = A. | last21 = Steele | first21 = R. P. | last22 = Rassolov | first22 = V. A. | last23 = Maslen | first23 = P. E. | last24 = Korambath | first24 = P. P. | last25 = Adamson | first25 = R. D. | last26 = Austin | first26 = B. | last27 = Baker | first27 = J. | last28 = Byrd | first28 = E. F. | last29 = Dachsel | first29 = H. | last30 = Doerksen | first30 = R. J. | display-authors = 29 }}</ref><ref>{{Cite journal|last1=Shao|first1=Yihan|last2=Gan|first2=Zhengting|last3=Epifanovsky|first3=Evgeny|last4=Gilbert|first4=Andrew T. B.|last5=Wormit|first5=Michael|last6=Kussmann|first6=Joerg|last7=Lange|first7=Adrian W.|last8=Behn|first8=Andrew|last9=Deng|first9=Jia|last10=Feng|first10=Xintian|last11=Ghosh|first11=Debashree|date=2015-01-17|title=Advances in molecular quantum chemistry contained in the Q-Chem 4 program package|url=https://doi.org/10.1080/00268976.2014.952696|journal=Molecular Physics|volume=113|issue=2|pages=184–215|doi=10.1080/00268976.2014.952696|bibcode=2015MolPh.113..184S |s2cid=4252077 |issn=0026-8976}}</ref><ref>{{Cite journal|last1=Epifanovsky|first1=Evgeny|last2=Gilbert|first2=Andrew T. B.|last3=Feng|first3=Xintian|last4=Lee|first4=Joonho|last5=Mao|first5=Yuezhi|last6=Mardirossian|first6=Narbe|last7=Pokhilko|first7=Pavel|last8=White|first8=Alec F.|last9=Coons|first9=Marc P.|last10=Dempwolff|first10=Adrian L.|last11=Gan|first11=Zhengting|date=2021-08-23|title=Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package|journal=The Journal of Chemical Physics|volume=155|issue=8|pages=084801|doi=10.1063/5.0055522|pmid=34470363 |pmc=9984241 |bibcode=2021JChPh.155h4801E |issn=0021-9606|doi-access=free}}</ref> featuring a variety of established and new methods implemented using innovative algorithms that enable fast calculations of large systems on various computer architectures, from laptops and regular lab workstations to midsize clusters, HPCC, and [[Cloud Computing|cloud computing]] using [[density functional theory|density functional]] and wave-function based approaches. It offers an integrated graphical interface and input generator; a large selection of functionals and correlation methods, including methods for electronically excited states and open-shell systems; solvation models; and wave-function analysis tools. In addition to serving the [[computational chemistry]]<ref name='compchem'>{{cite book | title =Computational Chemistry: A Practical Guide for Applying Techniques to Real World Problems| first1= David C. | last1= Young | publisher= Wiley-Interscience | year= 2001 | isbn= 978-0-471-33368-5 | doi= 10.1002/0471220655|chapter=Appendix A. A.2.7 Q-Chem |page= 339}}</ref> community, Q-Chem also provides a versatile code development platform.

==History==

Q-Chem software is maintained and distributed by Q-Chem, Inc.,<ref name='qc.url' /> located in Pleasanton, California, USA. It was founded in 1993 as a result of disagreements within the [[Gaussian (software)|Gaussian]] company that led to the departure (and subsequent "banning") of [[John Pople]] and a number of his students and postdocs (see [[Gaussian (software)#License controversy|Gaussian License Controversy]]<ref name='bbg.url'>[http://www.bannedbygaussian.org Banned By Gaussian]</ref>).<ref name='qc.url' /><ref name='qc.engine'>{{cite journal |last1=Krylov |first1=Anna I. |last2=Gill |first2=Peter M.W. |title=Q-Chem: an engine for innovation |journal=Wiley Interdisciplinary Reviews: Computational Molecular Science |date=May 2013 |volume=3 |issue=3 |pages=317–326 |doi=10.1002/wcms.1122|s2cid=16713704 }}</ref>

The first lines of the Q-Chem code were written by [[Peter Gill (chemist)|Peter Gill]], at that time a postdoc of [[John Pople|Pople]], during a winter vacation (December 1992) in Australia. Gill was soon joined by Benny Johnson (a [[John Pople|Pople]] graduate student) and Carlos Gonzalez (another [[John Pople|Pople]] postdoc), but the latter left the company shortly thereafter. In mid-1993, [[Martin Head-Gordon]], formerly a [[John Pople|Pople]] student, but at that time on the [[University of California, Berkeley|Berkeley]] tenure track, joined the growing team of academic developers.<ref name='qc.url' /><ref name='qc.engine' />

[[File:Q-Chem Postcard.jpg|thumb|Postcard advertising the release of Q-Chem 1.0.]]
<!-- Deleted image removed: [[File:Citations-to-qchem-papers.jpg|thumb|Fig. 2. Citations of the two Q-Chem papers<ref name='QC2.0' /><ref name='QC3.0' /> reached 200 per year in 2010, and is growing (as reported by ISI Web of Science).]] -->
In preparation for the first commercial release, the company hired Eugene Fleischmann as marketing director and acquired its URL www.q-chem.com in January 1997.  The first commercial product, Q-Chem 1.0, was released in March 1997. Advertising postcards celebrated the release with the proud headline, "Problems which were once impossible are now routine"; however, version 1.0 had many shortcomings, and a wit once remarked that the words "impossible" and "routine" should probably be interchanged!<ref name='qc.engine' /> However, vigorous code development continued, and by the following year Q-Chem 1.1 was able to offer most of the basic [[Quantum chemistry|quantum chemical]] functionality as well as a growing list of features (the continuous fast multipole method, J-matrix engine, COLD PRISM for integrals, and G96 [[density functional theory|density functional]], for example) that were not available in any other package.<ref name='qc.url' /><ref name='qc.engine' />

Following a setback when Johnson left, the company became more decentralized, establishing and cultivating relationships with an ever-increasing circle of research groups in universities around the world. In 1998, [[Henry F. Schaefer, III|Fritz Schaefer]] accepted an invitation to join the Board of Directors and, early in 1999, as soon as his non-compete agreement with [[Gaussian (software)|Gaussian]] had expired, [[John Pople]] joined as both a Director and code developer.<ref name='qc.url' /><ref name='qc.engine' />

In 2000, Q-Chem established a collaboration with Wavefunction Inc., which led to the incorporation of Q-Chem as the [[Ab initio quantum chemistry methods|ab initio]] engine in all subsequent versions of the Spartan package. The Q-Chem Board was expanded in March 2003 with the addition of [[Anna Krylov]] and Jing Kong.  In 2012, John Herbert joined the Board and [[Henry F. Schaefer, III|Fritz Schaefer]] became a Member Emeritus. The following year, Shirin Faraji joined the Board; [[Peter Gill (chemist)|Peter Gill]], who had been President of Q-Chem since 1988, stepped down; and [[Anna Krylov]] became the new president. 
In 2022-23 Yuezhi Mao and Joonho Lee joined the board.
The active Board of Directors currently consists of Lee, Mao, Faraji, [[Peter Gill (chemist)|Gill]] (past-President), Herbert, [[Anna Krylov|Krylov]] (President), and Hilary Pople ([[John Pople|John's]] daughter). [[Martin Head-Gordon]] remains a Scientific Advisor to the Board.<ref name='qc.url' /><ref name='qc.engine' />

Currently, there are thousands of Q-Chem licenses in use, and Q-Chem's user base is expanding, as illustrated by citation records for releases 2.0, 3.0, and 4.0, which reached 400 per year in 2016 (see Figure 2).<ref name='qc.engine' /> [[File:Citations.jpg|thumb|Fig. 2. Citations to Q-Chem: 2001 to 2019.]]  Q-Chem has been used as an engine in high-throughput studies, such as the Harvard [[Clean Energy Project]],<ref name="hcep">{{Cite web|title=The Clean Energy Project|url=http://cleanenergy.harvard.edu/|url-status=dead|archive-url=https://web.archive.org/web/20110403151651/http://cleanenergy.harvard.edu/|archive-date=2011-04-03|access-date=2012-02-10}}</ref> in which about 350,000 calculations were performed daily on the IBM [[World Community Grid]].
[[File:Q-Chem Developer Activity (2019).png|thumb|Figure 3. Statistics of Q-Chem developer activity since 2006. Top chart: Total number of code commits (height of bars) and number of developers contributing (color of bar) by month.  Bottom chart: Growth of developer base, showing existing and new developers each month. A steady growth of the developer base can be seen. The inset depicts the total number of commits by the 50 most-prolific developers, showing contributions by full-time team (> 2000 commits), the core developer team (500–2000 commits), and non-core developers (< 500 commits).]]
Innovative algorithms and new approaches to electronic structure have been enabling cutting-edge scientific discoveries. This transition, from in-house code to major electronic structure engine, has become possible due to contributions from numerous scientific collaborators; the Q-Chem business model encourages broad developer participation.  Q-Chem defines its genre as open-teamware:<ref name="qc.engine" /> its source code is open to a large group of developers. In addition, some Q-Chem modules are distributed as open source.<ref name="qc.engine" />  Since 1992, over 400 man- (and woman-) years have been devoted to code development. Q-Chem 5.2.2, released in December 2019, consists of 7.5 million lines of code, which includes contributions by more than 300 active developers (current estimate is 312).<ref name="qc.url">{{Cite web|url=http://www.q-chem.com/|title=Quantum Computational Software; Molecular Modeling; Visualization|website=www.q-chem.com|access-date=2020-01-22}}</ref><ref name="qc.engine" /> See Figure 3.

==Features==
Q-Chem can perform a number of general quantum chemistry calculations, such as [[Hartree–Fock method|Hartree–Fock]], [[density functional theory]] (DFT) including time-dependent DFT ([[Time-dependent density functional theory|TDDFT]]), [[Møller–Plesset perturbation theory]] (MP2), [[coupled cluster]] (CC), equation-of-motion coupled-cluster (EOM-CC),<ref name='eom-krylov' /><ref name='eom-sneskov' /><ref name='eom-bartlett' /> [[configuration interaction]] (CI), algebraic diagrammatic construction (ADC), and other advanced electronic structure methods. Q-Chem also includes [[QM/MM]] functionality. Q-Chem 4.0 and higher releases come with the graphical user interface, IQMol, which includes a hierarchical input generator, a molecular builder, and general visualization capabilities (MOs, densities, molecular vibrations, reaction pathways, etc.). IQMol is developed by Andrew Gilbert (in coordination with Q-Chem) and is distributed as free open-source software.  IQmol is written using the Qt libraries, enabling it to run on a range of platforms, including OS X, Widows, and Linux. It provides an intuitive environment to set up, run, and analyze Q-Chem calculations. It can also read and display a variety of file formats, including the widely available formatted checkpoint format. A complete, up-to-date list of features is published on the Q-Chem website and in the user manual.<ref name="qc.url" />

In addition, Q-Chem is interfaced with WebMO and is used as the computing engine in [[Spartan (chemistry software)|Spartan]], or as a back-end to [[CHARMM]], [[GROMACS]], [[NAMD]], and ChemShell. Other popular visualization programs such as [[Jmol]] and [[Molden]] can also be used.

In 2018, Q-Chem established a partnership with BrianQC, produced by StreamNovation, Ltd., a new integral engine exploiting the computational power of GPUs.  The BrianQC plug-in speeds up Q-Chem calculations by taking advantage of GPUs on mixed architectures, which is highly efficient for simulating large molecules and extended systems.  BrianQC is the first GPU Quantum Chemistry software capable of calculating high angular momentum orbitals.

===Ground State Self-Consistent Field Methods===
*Restricted, unrestricted, and restricted open-shell formulations
*Analytical first and second derivatives for geometry optimizations, harmonic frequency analysis, and ab initio molecular dynamics
*Efficient algorithms for fast convergence
*Variety of guess options (including MOM)

===Density functional theory===
*Variety of local, GGA, mGGA, hybrid, double-hybrid, dispersion-corrected, range separated functionals (energies and analytic first and second derivatives)
*TDDFT and spin-flip-TDDFT formulations (energies, gradients, and frequencies)
*Constrained DFT

===Innovative algorithms for faster performance and reduced scaling of integral calculations, HF/DFT and many-body methods===
*[[Dual basis]]
*Resolution of identity
*Cholesky decomposition of electron-repulsion integrals
*[[Continuous Fast Multipole Method]] (CFMM)
*Fast numerical integration of exchange-correlation with mrXC (multiresolution exchange-correlation)
*Linear-scaling HF-exchange method (LinK)
*Fourier transform Coulomb method (FTC)
*COLD PRISM and J-matrix engine
*Mixed-precision arithmetic for correlated methods<ref name="Pokhilko 4088–4096">{{Cite journal|last1=Pokhilko|first1=Pavel|last2=Epifanovsky|first2=Evgeny|last3=Krylov|first3=Anna I.|date=2018-08-14|title=Double Precision Is Not Needed for Many-Body Calculations: Emergent Conventional Wisdom|journal=Journal of Chemical Theory and Computation|language=en|volume=14|issue=8|pages=4088–4096|doi=10.1021/acs.jctc.8b00321|pmid=29969560|s2cid=49679144 |issn=1549-9618}}</ref>

===Post Hartree–Fock methods===
*MP2<ref name = 'MP2'>{{cite journal  |author1=Chr. Møller  |author2=M. S. Plesset  |name-list-style=amp | title = Note on an Approximation Treatment form Many-Electron Systems | journal = Physical Review | volume = 46 | pages = 618–622 | date = October 1934 | doi = 10.1103/PhysRev.46.618  | issue = 7 | bibcode=1934PhRv...46..618M|url=https://authors.library.caltech.edu/1753/1/MOLpr34.pdf  }}</ref><ref>{{cite journal | doi = 10.1016/0009-2614(88)85250-3 | title = MP2 energy evaluation by direct methods | year = 1988 | last1 = Head-Gordon | first1 = Martin | last2 = Pople | first2 = John A. | last3 = Frisch | first3 = Michael J. | journal = Chemical Physics Letters | volume = 153 | issue = 6 | pages = 503–506 | bibcode=1988CPL...153..503H}}</ref> (including RI-MP2,<ref>{{cite journal  |author1=Martin Feyereisena, George Fitzgeralda  |author2=Andrew Komornickib  |name-list-style=amp | title = Scaled Second-Order Perturbation Corrections to Configuration Interaction Singles: Efficient and Reliable Excitation Energy Methods | journal = Chemical Physics Letters | volume = 208 | issue = 5–6 | pages = 359–363 | date = May 10, 1993 | doi = 10.1016/0009-2614(93)87156-W |bibcode = 1993CPL...208..359F }}</ref><ref>{{cite journal  |author1=Florian Weigend  |author2=Marco Häser  |name-list-style=amp | title = RI-MP2: first derivatives and global consistency  | journal = Theoretical Chemistry Accounts | volume = 97 | issue = 1–4 | pages = 331–340 | date = October 13, 1997 | doi = 10.1007/s002140050269|s2cid=97649855 }}</ref><ref>{{cite journal  |author1=Robert A. Distasio JR. |author2=Ryan P. Steele |author3=Young Min Rhee |author4=Yihan Shao |author5=Martin Head-Gordon  |name-list-style=amp | title = An improved algorithm for analytical gradient evaluation in resolution-of-the-identity second-order Møller-Plesset perturbation theory: Application to alanine tetrapeptide conformational analysis | journal = Journal of Computational Chemistry | volume = 28 | pages = 839–856 | date = April 15, 2007 | doi = 10.1002/jcc.20604  |pmid=17219361 | issue = 5|s2cid=8438511 }}</ref> energies and analytic gradients)
*SCS, SOS-MP2, and OO-MP2
*CCD, [[Quadratic configuration interaction|QCISD]], CCSD, OOCCD, VOOCCD
*(T), (2), (dT), and (fT) corrections
*EOM-XX-CCSD methods for open-shell and electronically excited species (XX=EE, SF, IP, EA, DIP, DEA, 2SF; energies, properties, and gradients for most methods),<ref name='eom-krylov'>{{cite journal | author=A.I. Krylov | title= Equation-of-motion coupled-cluster methods for open-shell and electronically excited species: The hitchhiker's guide to Fock space | journal = Annual Review of Physical Chemistry | year= 2008 | volume=59| pages=433–462|bibcode = 2008ARPC...59..433K |doi = 10.1146/annurev.physchem.59.032607.093602 | pmid=18173379| s2cid= 43449082 | url=https://pdfs.semanticscholar.org/d92f/81cfb1c3a4d11c0cf78138d42b10b93e75d0.pdf | archive-url=https://web.archive.org/web/20200218175643/https://pdfs.semanticscholar.org/d92f/81cfb1c3a4d11c0cf78138d42b10b93e75d0.pdf | url-status=dead | archive-date=2020-02-18 }}</ref><ref name='eom-sneskov'>{{cite journal |author1=K. Sneskov |author2=O. Christiansen | title= Excited state coupled cluster methods | journal=Wiley Interdisciplinary Reviews: Computational Molecular Science | year=2011}}</ref><ref name='eom-bartlett'>{{cite journal | author=R.J. Bartlett | title=Coupled-cluster theory and its equation-of-motion extensions |journal=Wiley Interdisciplinary Reviews: Computational Molecular Science |volume=2 | page=126 | year=2012 |doi=10.1002/wcms.76| s2cid=122135895 }}</ref> including complex-valued variants for treating resonances (states metastable with respect to electron detachment)<ref name="Pokhilko 4088–4096"/>
*Extensions of DFT and many-body methods to treat core-level states and related spectroscopies<ref>{{Citation|title=Webinar 36 - Core-level spectroscopy in Q-Chem 5.2 - Presented by Prof. Anna Krylov, USC| date=23 October 2019 |url=https://www.youtube.com/watch?v=JzniF5AwkZk |archive-url=https://ghostarchive.org/varchive/youtube/20211222/JzniF5AwkZk |archive-date=2021-12-22 |url-status=live|language=en|access-date=2020-01-12}}{{cbignore}}</ref>
*ADC methods
*CIS, TDDFT, CIS(D), and SOS-CIS(D) methods for excited states
*Variety of implicit solvent models
*Wave-function analysis tools enabled by libwfa developed by Felix Plasser and co-workers<ref>{{Cite journal|last1=Plasser|first1=Felix|last2=Wormit|first2=Michael|last3=Dreuw|first3=Andreas|date=2014-07-14|title=New tools for the systematic analysis and visualization of electronic excitations. I. Formalism|journal=The Journal of Chemical Physics|language=en|volume=141|issue=2|pages=024106|doi=10.1063/1.4885819|pmid=25027998|bibcode=2014JChPh.141b4106P |s2cid=28303702 |issn=0021-9606|url=http://pdfs.semanticscholar.org/cd81/ba3285b28c2bc2c3fe21422deb5a8a7b5968.pdf|archive-url=https://web.archive.org/web/20190305015828/http://pdfs.semanticscholar.org/cd81/ba3285b28c2bc2c3fe21422deb5a8a7b5968.pdf|url-status=dead|archive-date=2019-03-05}}</ref>

===QM/MM and QM/EFP methods for extended systems===
*Janus [[QM/MM]] interface
*YinYang Atom model without linked atoms
*ONIOM model
*[[Effective Fragment Potential Method|EFP method]] (including library of effective fragments, EFP interface with CC/EOM, DFT/TDDFT, and other methods)<ref name='efp-gordon'>{{cite journal |author1=M.S. Gordon |author2=M.A. Freitag |author3=P. Bandyopadhyay |author4=J.H. Jensen |author5=V. Kairys |author6=W.J. Stevens | title= The effective fragment potential method: A QM-based MM approach to modeling environmental effects in chemistry | journal = Journal of Physical Chemistry A | volume=105| page=203|year=2001 | doi=10.1021/jp002747h | issue=2|bibcode=2001JPCA..105..293G |url=http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1392&context=chem_pubs }}</ref><ref name='efp-gordon-ch'>{{cite book|title=Volume 3 of Annual Reports in Computational Chemistry|year=2007|publisher=Elsevier|pages=177–193|author=M.S. Gordon, L. Slipchenko, H.Li, J.H. Jensen|editor1=D.C. Spellmeyer |editor2=R. Wheeler |chapter=The effective fragment potential: A general method for predicting intermolecular interactions}}</ref><ref name='efp-slipchenko'>{{cite journal | author=L.V. Slipchenko |title=Solvation of the excited states of chromophores in polarizable environment: orbital relaxation versus polarization|journal=Journal of Physical Chemistry A|volume=114|year=2010 | doi=10.1021/jp101797a |pmid=20504011| issue=33|pages=8824–30|bibcode=2010JPCA..114.8824S}}</ref><ref name='efp-ghosh'>{{cite journal |author1=D. Ghosh |author2=D. Kosenkov |author3=V. Vanovschi |author4=C. Williams |author5=J. Herbert |author6=M.S. Gordon |author7=M. Schmidt |author8=L.V. Slipchenko |author9=A.I. Krylov |title=Non-covalent interactions in extended systems described by the effective fragment potential method: theory and application to nucleobase oligomers| journal=Journal of Physical Chemistry A | volume=114|year=2010 | doi=10.1021/jp107557p |pmid=21067134 | issue=48|pages=12739–12754 |bibcode=2010JPCA..11412739G |pmc=2997142 }}</ref>

==Version history==
Beginning with Q-Chem 2.0 only major releases versions are shown.

*Q-Chem 1.0: March 1997
*Q-Chem 1.1: 1997<ref name="QC1.1">{{cite book |author1=B.G. Johnson |author2=P.M.W. Gill |author3=M. Head-Gordon |author4=C.A. White |author5=D.R. Maurice |author6=T.R. Adams |author7=J. Kong |author8=M. Challacombe |author9=E. Schwegler |author10=M. Oumi |author11=C. Ochsenfeld |author12=N. Ishikawa |author13=J. Florian |author14=R.D. Adamson |author15=J.P. Dombroski |author16=R.L. Graham and A.Warshel | year=1997 | title= Q-Chem, Version 1.1 | publisher= Q-Chem, Inc| location= Pittsburgh}}</ref>
*Q-Chem 1.2 1998<ref name="QC1.2">{{cite book |author1=C.A. White |author2=J. Kong |author3=D.R. Maurice |author4=T.R. Adams |author5=J. Baker |author6=M. Challacombe |author7=E. Schwegler |author8=J.P. Dombroski |author9=C. Ochsenfeld |author10=M. Oumi |author11=T.R. Furlani |author12=J. Florian |author13=R.D. Adamson |author14=N. Nair |author15=A.M. Lee |author16=N. Ishikawa |author17=R.L. Graham |author18=A. Warshel |author19=B.G. Johnson |author20=P.M.W. Gill |author21=M. Head-Gordon | year=1998 | title=Q-Chem, Version 1.2 | publisher= Q-Chem, Inc | location= Pittsburgh}}</ref>
*Q-Chem 2.0: 2000<ref name="QC2.0" />
*Q-Chem 3.0: 2006<ref name="QC3.0" />
*Q-Chem 4.0: February 2012
*Q-Chem 5.0: June 2017
*Q-Chem 5.2.2: December 2019
*Q-Chem 5.3.2: December 2020
*Q-Chem 5.4: June 2021
*Q-Chem 5.4.1: August 2021
*Q-Chem 5.4.2: December 2021
*Q-Chen 6.0: July 2022 
*Q-Chem 6.1.0: December 2022
*Q-Chem 6.1.1: December 2023
*Q-Chem 6.2.0: May 2024
*Q-Chem 6.2.2: November 2024

==See also==
{{columns-list|colwidth=22em|
* [[List of quantum chemistry and solid state physics software|Quantum chemistry computer programs]]
* [[Amsterdam Density Functional|ADF]]
* [[CHARMM]]
* [[CP2K]]
* [[GAMESS (US)]]
* [[GAMESS (UK)]]
* [[Gaussian (software)]]
* [[MOLCAS]]
* [[MOLPRO]]
* [[MPQC]]
* [[NWChem]]
* [[ORCA (Quantum Chemistry Program)|ORCA]]
* [[PSI (computational chemistry)|Psi3]]
* [[Firefly (computer program)|Firefly]]
* [[Quantemol]]
* [[Spartan (chemistry software)|Spartan]]
* [[TeraChem]]
* [[TURBOMOLE]]
}}

==References==
{{reflist}}

==External links==
*{{Official website|http://www.q-chem.com/ |name=Q-Chem Inc.}}
*[http://www.iqmol.org IQmol]
*[http://www.wavefun.com/ Wavefunction, Inc., Spartan Graphical Interface accesses and includes Q-Chem computational Engines]
*[http://webmo.net WebMO]
*[https://www.brianqc.com/ BrianQC]

{{Chemistry software}}

[[Category:Computational chemistry software]]
[[Category:Chemistry software for Linux]]
[[Category:Science software that uses Qt]]
[[Category:Proprietary commercial software for Linux]]
[[Category:Proprietary software that uses Qt]]