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open-shell_coupled_cluster_theories [2020/06/11 18:17]
127.0.0.1 external edit
open-shell_coupled_cluster_theories [2020/10/20 11:15] (current)
qianli Clarify open-shell [T] treatment
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   * **''%%RCCSD(T), UCCSD(T)%%''** triples corrections are computed as defined by J. D. Watts, J. Gauss and R. J. Bartlett, [[https://dx.doi.org/10.1063/1.464480|J. Chem. Phys.]] **98**, 8718 (1993).   * **''%%RCCSD(T), UCCSD(T)%%''** triples corrections are computed as defined by J. D. Watts, J. Gauss and R. J. Bartlett, [[https://dx.doi.org/10.1063/1.464480|J. Chem. Phys.]] **98**, 8718 (1993).
-  * **''%%RCCSD[T], UCCSD[T]%%''** corrections are computed without contributions of single excitations (sometimes called CCSD+T(CCSD).+  * **''%%RCCSD[T], UCCSD[T]%%''** corrections are computed without contributions of single excitations [sometimes called CCSD+T(CCSD)]. These slightly differ from the [T] corrections defined by [[https://dx.doi.org/10.1063/1.464480|Watts et al.]] in that the contributions from $X^{ijk}_{abc}$ are not included.
   * **''%%RCCSD-T, UCCSD-T%%''** triples corrections are computed as defined by M. J. O. Deegan and P. J. Knowles, [[https://dx.doi.org/10.1016/0009-2614(94)00815-9|Chem. Phys. Lett.]] **227**, 321 (1994).   * **''%%RCCSD-T, UCCSD-T%%''** triples corrections are computed as defined by M. J. O. Deegan and P. J. Knowles, [[https://dx.doi.org/10.1016/0009-2614(94)00815-9|Chem. Phys. Lett.]] **227**, 321 (1994).
  
-In fact, all three contributions are always computed and printed. The following variables are used to store the results (here ''CCSD'' stands for either ''UCCSD'' or ''RCCSD''):+All three contributions are always computed and printed. The following variables are used to store the results (here ''CCSD'' stands for either ''UCCSD'' or ''RCCSD''):
  
   * **''ENERGY''** total energy for method specified in the input.   * **''ENERGY''** total energy for method specified in the input.
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   * **''%%ENERGT(3)%%''** total ''CCSD-T'' energy.   * **''%%ENERGT(3)%%''** total ''CCSD-T'' energy.
  
-It should be noted that in open-shell cases the triples energy slightly depends on the treatment of core orbitals. In Molpro pseudo-canonical alpha and beta spin orbitals ([[http://dx.doi.org/10.1016/S0009-2614(91)85118-G|Chem. Phys. Letters **186** (1991) 130]]) are generated by block-diagonalizing the corresponding Fock matrices in the space of valence orbitals, leaving frozen core orbitals untouched. Some other programs include the frozen core orbitals in the canonicalization and transformation. Because of core-valence mixing this leads to slightly different energies. Neither of the two methods can be regarded as better or more justified — it is just a matter of definition. However, the method in Molpro is more efficient since the subsequent integral transformation involves only valence orbitals and no core orbitals.+It should be noted that in open-shell cases the triples energy slightly depends on the treatment of core orbitals. In Molpro pseudo-canonical alpha and beta spin orbitals %%[%%[[http://dx.doi.org/10.1016/S0009-2614(91)85118-G|Chem. Phys. Lett.]] **186**, 130 (1991)] are generated by block-diagonalizing the corresponding Fock matrices in the space of valence orbitals, leaving frozen core orbitals untouched. Some other programs include the frozen core orbitals in the canonicalization and transformation. Because of core-valence mixing this leads to slightly different energies. Neither of the two methods can be regarded as better or more justified — it is just a matter of definition. However, the method in Molpro is more efficient since the subsequent integral transformation involves only valence orbitals and no core orbitals.
  
 ==== Open-Shell Coupled cluster calculation on CN ==== ==== Open-Shell Coupled cluster calculation on CN ====