Description
This method keyword requests a Quadratic CI calculation [ Pople87 J. A. Pople, M. Head-Gordon, and K. Raghavachari, “Quadratic configuration interaction - a general technique for determining electron correlation energies,” J. Chem. Phys., 87 (1987) 5968-75. DOI: ], including single and double substitutions. Note that this keyword requests only QCISD and does not include the triples correction [ Gauss88 J. Gauss and D. Cremer, “Analytical evaluation of energy gradients in quadratic configuration-interaction theory,” Chem. Phys. Lett., 150 (1988) 280-86. DOI: , Salter89 E. A. Salter, G. W. Trucks, and R. J. Bartlett, “Analytic Energy Derivatives in Many-Body Methods. I. First Derivatives,” J. Chem. Phys., 90 (1989) 1752-66. DOI: ] by default (see T in Options).
オプション
Options
T
Requests a Quadratic CI calculation including single and double substitutions with a triples contribution to the energy added [ Pople87 J. A. Pople, M. Head-Gordon, and K. Raghavachari, “Quadratic configuration interaction - a general technique for determining electron correlation energies,” J. Chem. Phys., 87 (1987) 5968-75. DOI: ].
E4T
Requests a Quadratic CI calculation including single and double substitutions with a triples contribution to the energy and also an evaluation of MP4 triples. Must be specified with the T option.
TQ
Requests a Quadratic CI calculation including single and double substitutions with an energy contribution from triples and quadruples [ Raghavachari90 K. Raghavachari, J. A. Pople, E. S. Replogle, and M. Head-Gordon, “Fifth Order Møller-Plesset Perturbation Theory: Comparison of Existing Correlation Methods and Implementation of New Methods Correct to Fifth Order,” J. Phys. Chem., 94 (1990) 5579-86. DOI: ] added.
SaveAmplitudes
Saves the converged amplitudes in the checkpoint file for use in a subsequent calculation (e.g., using a larger basis set). Using this option results in a very large checkpoint file, but also may significantly speed up later calculations.
ReadAmplitudes
Reads the converged amplitudes from the checkpoint file (if present). Note that the new calculation can use a different basis set, method (if applicable), etc. than the original one.
T1Diag
Computes the Q1 diagnostic of T. J. Lee and coworkers [ Lee89 T. J. Lee and P. R. Taylor, “A diagnostic for determining the quality of single-reference electron correlation methods,” Int. J. Quantum Chem., Quant. Chem. Symp., S23 (1989) 199-207. DOI: , Lee90 T. J. Lee, A. P. Rendell, and P. R. Taylor, “Comparison of the Quadratic Configuration Interaction and Coupled-Cluster Approaches to Electron Correlation Including the Effect of Triple Excitations,” J. Phys. Chem., 94 (1990) 5463-68. DOI: ]. Note that Q1 is analogous to the T1 diagnostic for CCSD when it is computed using QCISD instead of the Coupled Cluster method.
FC
All frozen core options are available with this keyword; a frozen core calculation is the default. See the discussion of the FC options for full information.
Conver=N
Sets the convergence calculations to 10-N on the energy and 10-(N-2) on the wavefunction. The default is N=7 for single points and N=8 for gradients.
MaxCyc=n
Specifies the maximum number of cycles. The default is 50.
適用範囲
Availability
Analytic energies and gradients for QCISD, numerical gradients for QCISD(T), and numerical frequencies for all methods.
関連キーワード
Related Keywords
実例
Examples
The predicted energy from a QCISD calculation appears in the output in the final QCISD iteration:
DE(CORR)= -.54999890D-01 E(CORR)= -.7501966245D+02
When QCISD(T) is specified, the preceding output is followed by the energy including the non-iterative triples contribution:
QCISD(T)= -.75019725718D+02