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dc.contributor.authorSharma, Sandeepen
dc.contributor.authorKnizia, Geralden
dc.contributor.authorGuo, Shengen
dc.contributor.authorAlavi, Alien
dc.date.accessioned2019-02-13T10:49:06Z
dc.date.available2019-02-13T10:49:06Z
dc.date.issued2017-02-14en
dc.identifier.issn1549-9618
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/289362
dc.description.abstractWe present two efficient and intruder-free methods for treating dynamic correlation on top of general multiconfiguration reference wave functions - including such as obtained by the density matrix renormalization group (DMRG) with large active spaces. The new methods are the second order variant of the recently proposed multireference linearized coupled cluster method (MRLCC) [ Sharma, S.; Alavi, A. J. Chem. Phys. 2015 , 143 , 102815 ] and of N-electron valence perturbation theory (NEVPT2), with expected accuracies similar to MRCI+Q and (at least) CASPT2, respectively. Great efficiency gains are realized by representing the first order wave function with a combination of internal contraction (IC) and matrix product state perturbation theory (MPSPT). With this combination, only third order reduced density matrices (RDMs) are required. Thus, we obviate the need for calculating (or estimating) RDMs of fourth or higher order; these had so far posed a severe bottleneck for dynamic correlation treatments involving the large active spaces accessible to DMRG. Using several benchmark systems, including first and second row containing small molecules, Cr2, pentacene, and oxo-Mn(Salen), we show that active spaces containing at least 30 orbitals can be treated using this method. On a single node, MRLCC2 and NEVPT2 calculations can be performed with over 550 and 1100 virtual orbitals, respectively. We also critically examine the errors incurred due to the three sources of errors introduced in the present implementation - calculating second order instead of third order energy corrections, use of internal contraction, and approximations made in the reference wave function due to DMRG.
dc.languageengen
dc.titleCombining Internally Contracted States and Matrix Product States To Perform Multireference Perturbation Theory.en
dc.typeArticle
prism.issueIdentifier2en
prism.publicationDate2017en
prism.publicationNameJ Chem Theory Computen
prism.volume13en
dc.identifier.doi10.17863/CAM.21653
dcterms.dateAccepted2017-01-06en
rioxxterms.versionofrecord10.1021/acs.jctc.6b00898en
rioxxterms.versionAM*
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserveden
rioxxterms.licenseref.startdate2017-02-14en
dc.contributor.orcidSharma, Sandeep [0000-0002-6598-8887]
dc.contributor.orcidAlavi, Ali [0000-0002-0654-9489]
dc.identifier.eissn1549-9626
rioxxterms.typeJournal Article/Reviewen
cam.issuedOnline2017-01-06en


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