{"id":"https://openalex.org/W1998705691","doi":"https://doi.org/10.1063/1.1679283","title":"PNO\u2013CI Studies of electron correlation effects. I. Configuration expansion by means of nonorthogonal orbitals, and application to the ground state and ionized states of methane","display_name":"PNO\u2013CI Studies of electron correlation effects. I. Configuration expansion by means of nonorthogonal orbitals, and application to the ground state and ionized states of methane","publication_year":1973,"publication_date":"1973-02-01","ids":{"openalex":"https://openalex.org/W1998705691","doi":"https://doi.org/10.1063/1.1679283","mag":"1998705691"},"language":"en","primary_location":{"id":"doi:10.1063/1.1679283","doi":"https://doi.org/10.1063/1.1679283","is_oa":false,"landing_page_url":"https://doi.org/10.1063/1.1679283","pdf_url":null,"source":{"id":"https://openalex.org/S77047749","display_name":"The Journal of Chemical Physics","issn_l":"0021-9606","issn":["0021-9606","1089-7690","1520-9032"],"is_oa":false,"is_in_doaj":false,"is_core":true,"listed_in":["anvur-scientific","cwts-core","dongbi-b","jufo-1","ki-jl-1","medline","norway-1","poland-100","russia-white-list-2","vabb-shw"],"host_organization":"https://openalex.org/P4310320257","host_organization_name":"American Institute of Physics","host_organization_lineage":["https://openalex.org/P4310320257"],"host_organization_lineage_names":["American Institute of Physics"],"type":"journal"},"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"The Journal of Chemical Physics","raw_type":"journal-article"},"parent_works":[],"lineage":["https://openalex.org/W1998705691"],"child_works_count":0,"type":"article","is_traditional":true,"indexed_in":["crossref"],"open_access":{"is_oa":false,"oa_status":"closed","oa_url":null,"any_repository_has_fulltext":false},"authorships":[{"author_position":"first","author":{"id":"https://openalex.org/A5080429301","display_name":"Wilfried Meyer","orcid":null,"observed_orcids":[]},"institutions":[{"id":"https://openalex.org/I100066346","display_name":"University of Stuttgart","ror":"https://ror.org/04vnq7t77","country_code":"DE","type":"education","lineage":["https://openalex.org/I100066346"]},{"id":"https://openalex.org/I1341412227","display_name":"IBM (United States)","ror":"https://ror.org/05hh8d621","country_code":"US","type":"company","lineage":["https://openalex.org/I1341412227"]}],"countries":["DE","US"],"is_corresponding":true,"raw_author_name":"Wilfried Meyer","raw_affiliation_strings":["IBM Research Laboratories, San Jose, California","Institut f\u00fcr Theoretische Physikalische Chemie, Universit\u00e4t Stuttgart, Germany"],"raw_orcid":null,"affiliations":[{"raw_affiliation_string":"IBM Research Laboratories, San Jose, California","institution_ids":["https://openalex.org/I1341412227"]},{"raw_affiliation_string":"Institut f\u00fcr Theoretische Physikalische Chemie, Universit\u00e4t Stuttgart, Germany","institution_ids":["https://openalex.org/I100066346"]}]}],"institutions":[],"countries_distinct_count":2,"institutions_distinct_count":2,"corresponding_author_ids":["https://openalex.org/A5080429301"],"corresponding_institution_ids":["https://openalex.org/I100066346","https://openalex.org/I1341412227"],"apc_list":{"value":3500,"currency":"USD","value_usd":3500},"apc_paid":null,"fwci":26.2442,"has_fulltext":false,"cited_by_count":1000,"citation_normalized_percentile":{"value":0.99991132,"is_in_top_1_percent":true,"is_in_top_10_percent":true},"cited_by_percentile_year":{"min":99,"max":100},"biblio":{"volume":"58","issue":"3","first_page":"1017","last_page":"1035"},"is_retracted":false,"is_paratext":false,"is_xpac":false,"primary_topic":{"id":"https://openalex.org/T10002","display_name":"Advanced Chemical Physics Studies","score":0.9961000084877014,"subfield":{"id":"https://openalex.org/subfields/3107","display_name":"Atomic and Molecular Physics, and Optics"},"field":{"id":"https://openalex.org/fields/31","display_name":"Physics and Astronomy"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},"topics":[{"id":"https://openalex.org/T10002","display_name":"Advanced Chemical Physics Studies","score":0.9961000084877014,"subfield":{"id":"https://openalex.org/subfields/3107","display_name":"Atomic and Molecular Physics, and Optics"},"field":{"id":"https://openalex.org/fields/31","display_name":"Physics and Astronomy"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T10523","display_name":"Atomic and Molecular Physics","score":0.0024999999441206455,"subfield":{"id":"https://openalex.org/subfields/3107","display_name":"Atomic and Molecular Physics, and Optics"},"field":{"id":"https://openalex.org/fields/31","display_name":"Physics and Astronomy"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}},{"id":"https://openalex.org/T12044","display_name":"Advanced Physical and Chemical Molecular Interactions","score":0.00039999998989515007,"subfield":{"id":"https://openalex.org/subfields/1606","display_name":"Physical and Theoretical Chemistry"},"field":{"id":"https://openalex.org/fields/16","display_name":"Chemistry"},"domain":{"id":"https://openalex.org/domains/3","display_name":"Physical Sciences"}}],"keywords":[{"id":"https://openalex.org/keywords/electron-correlation","display_name":"electron correlation","score":0.7429999709129333},{"id":"https://openalex.org/keywords/configuration-interaction","display_name":"configuration interaction","score":0.6830000281333923},{"id":"https://openalex.org/keywords/non-orthogonal-orbitals","display_name":"nonorthogonal orbitals","score":0.8820000290870667},{"id":"https://openalex.org/keywords/methane","display_name":"methane","score":0.5630000233650208},{"id":"https://openalex.org/keywords/ionized-states","display_name":"ionized states","score":0.6909999847412109},{"id":"https://openalex.org/keywords/correlation-energy","display_name":"correlation energy","score":0.628000020980835},{"id":"https://openalex.org/keywords/ionization-potential","display_name":"ionization potential","score":0.8209999799728394},{"id":"https://openalex.org/keywords/photoelectron-spectra","display_name":"photoelectron spectra","score":0.8999999761581421},{"id":"https://openalex.org/keywords/anharmonicity","display_name":"anharmonicity","score":0.6949999928474426},{"id":"https://openalex.org/keywords/bond-lengths","display_name":"bond lengths","score":0.5170000195503235},{"id":"https://openalex.org/keywords/harmonics","display_name":"harmonics","score":0.6430000066757202}],"concepts":[{"id":"https://openalex.org/C189394030","wikidata":"https://www.wikidata.org/wiki/Q53860","display_name":"Atomic orbital","level":3,"score":0.7141577005386353},{"id":"https://openalex.org/C2777529809","wikidata":"https://www.wikidata.org/wiki/Q900672","display_name":"Configuration interaction","level":3,"score":0.6739947199821472},{"id":"https://openalex.org/C113603373","wikidata":"https://www.wikidata.org/wiki/Q2362761","display_name":"Wave function","level":2,"score":0.6684020757675171},{"id":"https://openalex.org/C184779094","wikidata":"https://www.wikidata.org/wiki/Q26383","display_name":"Atomic physics","level":1,"score":0.666706383228302},{"id":"https://openalex.org/C68030841","wikidata":"https://www.wikidata.org/wiki/Q172948","display_name":"Bohr model","level":2,"score":0.6600180864334106},{"id":"https://openalex.org/C147192597","wikidata":"https://www.wikidata.org/wiki/Q483769","display_name":"Ionization energy","level":4,"score":0.6282826662063599},{"id":"https://openalex.org/C35052450","wikidata":"https://www.wikidata.org/wiki/Q2733663","display_name":"Electronic correlation","level":3,"score":0.6255191564559937},{"id":"https://openalex.org/C69523127","wikidata":"https://www.wikidata.org/wiki/Q4480008","display_name":"Ground state","level":2,"score":0.6021385788917542},{"id":"https://openalex.org/C147120987","wikidata":"https://www.wikidata.org/wiki/Q2225","display_name":"Electron","level":2,"score":0.5745577216148376},{"id":"https://openalex.org/C185592680","wikidata":"https://www.wikidata.org/wiki/Q2329","display_name":"Chemistry","level":0,"score":0.509166419506073},{"id":"https://openalex.org/C121332964","wikidata":"https://www.wikidata.org/wiki/Q413","display_name":"Physics","level":0,"score":0.49098899960517883},{"id":"https://openalex.org/C198291218","wikidata":"https://www.wikidata.org/wiki/Q190382","display_name":"Ionization","level":3,"score":0.44502097368240356},{"id":"https://openalex.org/C38649801","wikidata":"https://www.wikidata.org/wiki/Q107414","display_name":"Valence electron","level":3,"score":0.4206409752368927},{"id":"https://openalex.org/C62520636","wikidata":"https://www.wikidata.org/wiki/Q944","display_name":"Quantum mechanics","level":1,"score":0.3047003746032715},{"id":"https://openalex.org/C181500209","wikidata":"https://www.wikidata.org/wiki/Q215328","display_name":"Excited state","level":2,"score":0.11109727621078491},{"id":"https://openalex.org/C145148216","wikidata":"https://www.wikidata.org/wiki/Q36496","display_name":"Ion","level":2,"score":0.06215742230415344}],"mesh":[],"locations_count":1,"locations":[{"id":"doi:10.1063/1.1679283","doi":"https://doi.org/10.1063/1.1679283","is_oa":false,"landing_page_url":"https://doi.org/10.1063/1.1679283","pdf_url":null,"source":{"id":"https://openalex.org/S77047749","display_name":"The Journal of Chemical Physics","issn_l":"0021-9606","issn":["0021-9606","1089-7690","1520-9032"],"is_oa":false,"is_in_doaj":false,"is_core":true,"listed_in":["anvur-scientific","cwts-core","dongbi-b","jufo-1","ki-jl-1","medline","norway-1","poland-100","russia-white-list-2","vabb-shw"],"host_organization":"https://openalex.org/P4310320257","host_organization_name":"American Institute of Physics","host_organization_lineage":["https://openalex.org/P4310320257"],"host_organization_lineage_names":["American Institute of Physics"],"type":"journal"},"license":null,"license_id":null,"version":"publishedVersion","is_accepted":true,"is_published":true,"raw_source_name":"The Journal of Chemical Physics","raw_type":"journal-article"}],"best_oa_location":null,"sustainable_development_goals":[],"study_designs":[],"awards":[],"funders":[],"has_content":{"pdf":false,"grobid_xml":false},"content_urls":null,"referenced_works_count":97,"referenced_works":["https://openalex.org/W170697199","https://openalex.org/W290423010","https://openalex.org/W1490570686","https://openalex.org/W1575110448","https://openalex.org/W1967237818","https://openalex.org/W1969586038","https://openalex.org/W1973312790","https://openalex.org/W1974446785","https://openalex.org/W1976399060","https://openalex.org/W1977614874","https://openalex.org/W1978373966","https://openalex.org/W1981931404","https://openalex.org/W1983981378","https://openalex.org/W1984358519","https://openalex.org/W1986248713","https://openalex.org/W1986751761","https://openalex.org/W1986781840","https://openalex.org/W1986988688","https://openalex.org/W1991760834","https://openalex.org/W1992947806","https://openalex.org/W1994879105","https://openalex.org/W1996330842","https://openalex.org/W1996704062","https://openalex.org/W1997131853","https://openalex.org/W1997775783","https://openalex.org/W2002045868","https://openalex.org/W2012846246","https://openalex.org/W2012932237","https://openalex.org/W2013455311","https://openalex.org/W2015597143","https://openalex.org/W2017643857","https://openalex.org/W2018974473","https://openalex.org/W2021337984","https://openalex.org/W2022319193","https://openalex.org/W2023497750","https://openalex.org/W2025301220","https://openalex.org/W2028007212","https://openalex.org/W2031653903","https://openalex.org/W2032603153","https://openalex.org/W2035093537","https://openalex.org/W2035483442","https://openalex.org/W2038618182","https://openalex.org/W2040514068","https://openalex.org/W2041164828","https://openalex.org/W2043098025","https://openalex.org/W2045021855","https://openalex.org/W2046418520","https://openalex.org/W2048791372","https://openalex.org/W2050741863","https://openalex.org/W2050764527","https://openalex.org/W2051588719","https://openalex.org/W2060212575","https://openalex.org/W2060373595","https://openalex.org/W2060442744","https://openalex.org/W2063364288","https://openalex.org/W2066115936","https://openalex.org/W2069146211","https://openalex.org/W2070176804","https://openalex.org/W2073593610","https://openalex.org/W2077132360","https://openalex.org/W2077261815","https://openalex.org/W2077509184","https://openalex.org/W2077624619","https://openalex.org/W2078193195","https://openalex.org/W2078960909","https://openalex.org/W2080984699","https://openalex.org/W2081587283","https://openalex.org/W2085700520","https://openalex.org/W2085934332","https://openalex.org/W2090993263","https://openalex.org/W2091733454","https://openalex.org/W2091828981","https://openalex.org/W2093723124","https://openalex.org/W2093890890","https://openalex.org/W2108980885","https://openalex.org/W2109931506","https://openalex.org/W2113448580","https://openalex.org/W2115878464","https://openalex.org/W2117302902","https://openalex.org/W2130213234","https://openalex.org/W2131800859","https://openalex.org/W2132347175","https://openalex.org/W2139430604","https://openalex.org/W2159449161","https://openalex.org/W2162172054","https://openalex.org/W2170095176","https://openalex.org/W2222517232","https://openalex.org/W2291552707","https://openalex.org/W2314127255","https://openalex.org/W2319309913","https://openalex.org/W2331582019","https://openalex.org/W2333944422","https://openalex.org/W2335578844","https://openalex.org/W2622167022","https://openalex.org/W3092905708","https://openalex.org/W4230151690","https://openalex.org/W4251454093"],"related_works":["https://openalex.org/W2322724852","https://openalex.org/W1985502232","https://openalex.org/W2060549967","https://openalex.org/W2015701404","https://openalex.org/W2108980885","https://openalex.org/W1973804168","https://openalex.org/W3092650793","https://openalex.org/W2018217082","https://openalex.org/W3118253989","https://openalex.org/W2065506137"],"abstract_inverted_index":{"It":[0],"is":[1,34,65,73,115,132,152,167,186,234,237,255,279],"shown":[2],"that":[3,197,281],"the":[4,7,21,35,39,83,91,104,109,112,121,128,137,157,182,198,202,214,224,241,250,264,272,282,289],"convergence":[5],"of":[6,10,43,61,70,98,111,127,159,232,244,253,271],"configuration":[8],"expansion":[9,42],"a":[11,44,76,285],"many-electron":[12,36],"wavefunction":[13,31],"may":[14,50],"be":[15,51,170],"drastically":[16],"improved":[17],"without":[18],"significantly":[19],"complicating":[20],"energy":[22,110,131,151,230],"matrix":[23],"elements":[24],"by":[25,53,227],"using":[26],"partially":[27],"non-orthogonal":[28],"orbitals.":[29],"The":[30,47,142,162,210,219,229],"thus":[32],"obtained":[33],"analog":[37],"to":[38,90,108,169,175,179,191,201,213,239,247,257],"natural":[40],"orbital":[41],"two-electron":[45],"wavefunction.":[46],"orbitals":[48,55,64],"involved":[49],"approximated":[52],"pseudonatural":[54],"(``PNO\u2013CI''),":[56],"and":[57,94,146,181,236,274,277],"an":[58],"efficient":[59],"way":[60],"calculating":[62],"these":[63],"presented.":[66],"An":[67],"approximate":[68],"treatment":[69],"multiple":[71],"substitutions":[72],"discussed":[74],"yielding":[75],"coupled":[77],"electron":[78],"pair":[79],"theory":[80],"formulated":[81],"within":[82],"CI":[84],"scheme.":[85],"These":[86,194],"methods":[87],"are":[88,217,267],"applied":[89],"ground":[92,113],"state":[93,114],"three":[95],"ionized":[96],"states":[97],"methane.":[99],"Including":[100],"only":[101],"double":[102],"substitutions,":[103],"computed":[105],"upper":[106],"bound":[107],"\u221240.4584":[116],"hartree,":[117],"i.e.":[118],"0.057":[119],"above":[120],"experimental":[122],"nonrelativistic":[123],"energy.":[124],"About":[125],"83%":[126],"total":[129],"correlation":[130,150,211],"accounted":[133],"for":[134],"variationally,":[135],"whereas":[136],"coupled-pair":[138,275],"approximation":[139],"yields":[140],"89%.":[141],"ratio":[143],"between":[144],"intraorbital":[145],"interorbital":[147],"valence":[148],"shell":[149],"calculated":[153],"as":[154],"1.56":[155],"in":[156,165],"case":[158],"localized":[160],"electrons.":[161],"equilibrium":[163],"distance":[164],"CH4":[166],"found":[168,256],"shifted":[171],"from":[172,188,223],"2.046":[173],"bohr":[174,177],"2.061":[176],"due":[178],"correlation,":[180],"harmonic":[183],"frequency":[184],"\u03bd1":[185],"reduced":[187],"3149":[189],"cm\u22121":[190],"3037":[192],"cm\u22121.":[193],"results":[195,266],"indicate":[196],"anharmonicity":[199],"corrections":[200],"observed":[203,225],"values":[204,226],"have":[205,258],"probably":[206],"been":[207],"over":[208,288],"estimated.":[209],"contributions":[212],"ionization":[215],"potentials":[216,221],"analyzed.":[218],"theoretical":[220],"differ":[222],"1%\u20132%.":[228],"surface":[231],"CH4+":[233,254],"investigated":[235],"used":[238],"discuss":[240],"photoelectron":[242],"spectrum":[243],"CH4.":[245],"Contrary":[246],"previous":[248],"work,":[249],"lowest":[251],"minimum":[252],"C2v":[259],"symmetry.":[260],"In":[261],"all":[262],"applications":[263],"variational":[265],"compared":[268],"with":[269],"those":[270],"independent-pair":[273],"approaches,":[276],"it":[278],"concluded":[280],"latter":[283],"represents":[284],"definite":[286],"improvement":[287],"first":[290],"two.":[291]},"counts_by_year":[{"year":2026,"cited_by_count":11},{"year":2025,"cited_by_count":12},{"year":2024,"cited_by_count":11},{"year":2023,"cited_by_count":10},{"year":2022,"cited_by_count":12},{"year":2021,"cited_by_count":13},{"year":2020,"cited_by_count":20},{"year":2019,"cited_by_count":10},{"year":2018,"cited_by_count":15},{"year":2017,"cited_by_count":15},{"year":2016,"cited_by_count":14},{"year":2015,"cited_by_count":15},{"year":2014,"cited_by_count":15},{"year":2013,"cited_by_count":16},{"year":2012,"cited_by_count":14}],"updated_date":"2026-11-07T11:25:07.637180","created_date":"2016-06-24T00:00:00"}