Frequently Asked Questions about SAC-CI

 

1. How to start the SAC-CI calculations

Q. What can I study with the SAC-CI program on Gaussian 03?

Q. Learning the SAC-CI method: methodology and computations.

Q. Are there sample inputs for the SAC-CI calculations?

Q. How to determine number of solution in each symmetry?

 

2. Choice of Basis sets in the SAC-CI calculations

Q. Valence and Rydberg states of organic aromatic compounds

Q. Excited and ionized states of the porphyrin compounds

Q. Excited and ionized states of ethylene

Q. Excited states of transition metal complexes

Q. Shake-up ionized states in valence ionization spectra

Q. Core-electron excitation and ionization

Q. Metal surfaces

Q. Geometry optimization of large molecules

Q. Hyperfine splitting constants

 

3. Method and Accuracy

Q. Levels of accuracy in the SAC/SAC-CI calculations

Q. How to set the threshold for the selection?

Q. Dimension (number of the excitation operators) of the SAC/SAC-CI calculations

Q. What is the default in SAC-CI calculation?

Q. What is the difference between EOM-CC, CC-LRT, and SAC-CI?

Q. How to calculate the ground and excited states of molecules having open-shell ground state? With ionization or with electron-attachment?

Q. Is it possible to calculate the excited states of species with a triplet spin ground state, e.g. oxygen atom or oxygen molecule, and what does the input look like?

Q. Is it possible to calculate the bond energies, A-B → A + B (A, B: radical) using the SAC/SAC-CI method with the following procedure?

 

4. Large system

Q. Job terminates at integral transformation (Overlay8) due to full of disk space.

Q. Job terminates with "No memory left for SECI diagonalization". I specified "MaxR2Op=100000000".

Q. Perturbation selection takes time and the job does not proceed.

Q. In the step "PRES", the job terminates with the message,"the Number of R2 operators is larger than ...".

Q. How to determine the memory size with the option "%mem" for SAC-CI calculation?

Q. In calculations with large active space. the calculation takes very long time to diagonalize the reference-CI matrix.

Q. Save core-memory by using Real*4 MO ERI (Electron Repulsion Integrals) in instead of the Real*8 one.

 

5. Potential energy surface

Q. Does the selection of the operators affect the smoothness of the potential surface?

Q. Potential curve for single-bond twisting.

 

6. Geometry optimization

Q. Initial geometry for the SAC-CI optimization

Q. Should I use geometry optimized by the SAC method for calculations of the vertical excitation energy with the SAC-CI method?

Q. MOs during the geometry optimization

Q. Number of solutions in the SAC-CI optimization

Q. PES and vibrational frequency calculations

Q. Is the MOD method dependent on the initial structure?

Q. Geometry optimization terminated at step "ZVECIT".

Q. How to check the convergence behavior in the SAC-CI optimization?

Q. How can we check the MOD method work properly?

Q. In a frequency calculation, large force (larger than the convergence threshold) was calculated. I have optimized the molecular geometry with SAC/SAC-CI method and the optimized geometry was used for the frequency calculation.

 

7. General-R

Q. When do we use the SAC-CI general-R method?

Q. How to generate the higher-order linked operators in the SAC-CI general-R calculations?

Q. What are the reference state and the active space for the perturbation selection in the general-R?

Q. How to determine the thresholds for the exponential generation of the higher-order excitation operators?

 

8. Core-electron excitations and ionizations

Q. Is there sample input for calculating core-electron processes?

Q. Why Rydberg basis sets are necessary in core-electron excitations and ionizations?

 

9. Relativistic effect

Q. How I can include the scalar relativistic effect into SAC-CI calculations?

Q. Spin-Orbit interaction included in the SAC-CI states as the first-order perturbation.

 

10. Property

Q. Sign of transition moment changes

Q. Can I calculate transition moment between the excited states?

Q. Is the SAC-CI method applicable to Circular Dichroism (CD) spectrum?

Q. Can we calculate the electrostatic properties with the SAC-CI relaxed density matrix?

Q. How to study hyperfine splitting constants (hfsc) with the SAC-CI method.

 

11. Other questions

Q. Is there explanation about the SAC-CI output?

Q. How can we understand the SAC-CI wave function in the output?

Q. What is the definition of the excitation energy? Is it the relative energy from the SAC state (closed-shell singlet state) or the lowest state in each spin-symmetry?

Q. Which kind of computational resources is necessary to perform SAC-CI calculations?

Q. Job terminates at generating the initial guess orbitals (Overlay4).