*F**requently 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. 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?

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

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. 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?

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*?

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

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