In this work,we investigate the performance of various equation-of-motion/linear-response coupled cluster(EOM/LR-CC)methods with an approximate treatment for triples on excitation energies(EEs)by comparing with EOM-CC...In this work,we investigate the performance of various equation-of-motion/linear-response coupled cluster(EOM/LR-CC)methods with an approximate treatment for triples on excitation energies(EEs)by comparing with EOM-CCSDT(SDT=single,double,triple excitations)results.The focus of this work is on singly-excited states with percentages of the single excitation part(R_(1),%)from CC3 between 50%and 80%,i.e.,excited states with a pronounced double excitation character.CC3 is shown to provide EEs that agree well with EOM-CCSDT results for such excited states.Moreover,reliable EEs can be obtained with EOM-CCSD(T)(a)^(*) and CCSDR(3)for excited states with R1 from CC3 larger than 80%.As for singly-excited states with R1 from CC3 between 80%and 50%,EEs with EOM-CCSD^(*),CCSDR(T)andδ-CR-EOM-CC(2,3)-D agree reasonably well with those of EOM-CCSDT.However,it is too costly to choose a proper method for singly-excited states based on R_(1) of CC3 since CC3 is a rather expensive method.On the other hand,our results show that difference between EEs with EOM-CCSD and EOM-CCSD(T)(a)*[ΔE_((T)(a)*)]correlates well with R1 from CC3 andΔE_((T)(a)*)is about 0.25 eV when R_(1)(CC3)is 80%.Appropriate methods to obtain reasonable EEs for singly-excited state can be chosen based on whetherΔE_((T)(a)*)is larger than 0.25 eV.展开更多
Within the localized molecular orbital description,the intra- and interorbital pair correlation energies calculated with the coupled cluster doubles (CCD) theory have been obtained for methane,ethane,propane,butane,is...Within the localized molecular orbital description,the intra- and interorbital pair correlation energies calculated with the coupled cluster doubles (CCD) theory have been obtained for methane,ethane,propane,butane,isobutane,pentane, isopentane and neopentane using the 6-31G * basis set. The results showed the quantitative transferability of pair correlation energies and gross orbital correlation energies within this series of molecules. Based on the gross orbital correlation energies of five sample alkanes (butane,isobutane,pentane,isopentane and neopentane),we have derived a simple linear relationship to estimate the CCD correlation energy for an arbitrary large alkane. The correlation energy predicted by this simple relationship remarkably recovers more than 98.9% of the exact CCD correlation energy for a number of alkanes containing six to eight carbon atoms. The relative stability of less branched isomers can be correctly predicted.展开更多
基金supported by the National Natural Science Foundation of China(Nos.21973063,21773160)。
文摘In this work,we investigate the performance of various equation-of-motion/linear-response coupled cluster(EOM/LR-CC)methods with an approximate treatment for triples on excitation energies(EEs)by comparing with EOM-CCSDT(SDT=single,double,triple excitations)results.The focus of this work is on singly-excited states with percentages of the single excitation part(R_(1),%)from CC3 between 50%and 80%,i.e.,excited states with a pronounced double excitation character.CC3 is shown to provide EEs that agree well with EOM-CCSDT results for such excited states.Moreover,reliable EEs can be obtained with EOM-CCSD(T)(a)^(*) and CCSDR(3)for excited states with R1 from CC3 larger than 80%.As for singly-excited states with R1 from CC3 between 80%and 50%,EEs with EOM-CCSD^(*),CCSDR(T)andδ-CR-EOM-CC(2,3)-D agree reasonably well with those of EOM-CCSDT.However,it is too costly to choose a proper method for singly-excited states based on R_(1) of CC3 since CC3 is a rather expensive method.On the other hand,our results show that difference between EEs with EOM-CCSD and EOM-CCSD(T)(a)*[ΔE_((T)(a)*)]correlates well with R1 from CC3 andΔE_((T)(a)*)is about 0.25 eV when R_(1)(CC3)is 80%.Appropriate methods to obtain reasonable EEs for singly-excited state can be chosen based on whetherΔE_((T)(a)*)is larger than 0.25 eV.
基金ProjectsupportedbytheNationalNaturalScienceFoundationofChina (No .2 0 0 73 0 2 0 )
文摘Within the localized molecular orbital description,the intra- and interorbital pair correlation energies calculated with the coupled cluster doubles (CCD) theory have been obtained for methane,ethane,propane,butane,isobutane,pentane, isopentane and neopentane using the 6-31G * basis set. The results showed the quantitative transferability of pair correlation energies and gross orbital correlation energies within this series of molecules. Based on the gross orbital correlation energies of five sample alkanes (butane,isobutane,pentane,isopentane and neopentane),we have derived a simple linear relationship to estimate the CCD correlation energy for an arbitrary large alkane. The correlation energy predicted by this simple relationship remarkably recovers more than 98.9% of the exact CCD correlation energy for a number of alkanes containing six to eight carbon atoms. The relative stability of less branched isomers can be correctly predicted.
