Download Describe the difference between the MCSCF and CISD

Typical Questions for Final Exam
Describe the difference between the MCSCF and CISD methods.
Imagine that you carried out HF calculations of a certain molecule and found that the orbital
energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied MO
(LUMO) are very close to each other. Now you need to improve your calculation by
including electron correlation. What type of electron correlation, dynamical or nondynamical, will be more important for this case and why? Choose one of the following three
methods for electron correlation calculations, MP2, CISD, or MCSCF, and explain your
choice.
Outline the Kohn-Sham Self Consistent Field method. In this outline, describe the main
ideas of density functional theory, two Hohenberg-Kohn theorems, and draw a flow chart
of the KS SCF procedure.
Describe the difference between LDA, GGA, and hybrid density functionals.
Explain the classification of partial atomic charges into Class I, Class II, Class III, and
Class IV. How the charges are calculated in the Mulliken population analysis?
Match the following calculations with the best method for them. Each method can be
used only once. Give a very brief reason for each choice. [Note: While the highest-level
method could be a good choice for any of the calculations, there is one superior
combination when each method has to be used once.]
Calculation
Method
Refine (optimize) the X-ray crystallographic
geometry of a protein
PM3
Electron affinity of ClO4
INDO/S
Electronic excitation energy for a transition
metal complex
HF/6-31G(d)
Energy difference between the boat and
chair conformation of hexane
HF/6-31+G(d)
Barrier for the interconversion of
the cis and trans isomers of C2H2Cl2
CHARMM force field
Describe Hückel theory. Illustrate application of this theory to the allyl system – write the
secular determinant and secular equations for this molecule.
What is Molecular Mechanics (MM)? What are the four main kinds of terms used in the
molecular mechanics force field? What are some advantages and disadvantages of MM?
Describe the difference between the MCSCF, configuration interaction, and MöllerPlesset perturbation theory methods. How would you decide which method would be
most appropriate for calculations of a particular molecule?
What molecular properties can be computed using the GAUSSIAN program and with
what kind of experimental data can they be compared? Take 1,2-dichlorobenzene as an
example and write GAUSSIAN input files for calculations of these properties (for input
files, you may write z-matrix only once and give different command lines for calculations
of various properties.
You need to calculate the standard heat of formation of chloroethane, C2H5Cl. Describe
how would you do these calculations if you know:
a) experimental heats of formation of C, H, and Cl atoms;
b) experimental heats of formation of ethane C2H6, methane CH4, and chloromethane
CH3Cl.
What theoretical methods would you use for the cases a) and b)?
Describe the Gaussian-2 (G2) method. What is its expected accuracy for energy
calculations? What is the main idea of G2?
What is the difference between trajectories and Monte-Carlo calculations in Molecular
Dynamics?
You study a bimolecular chemical reaction leading to a unimolecular product, A + B →
TS → C, and, using GAUSSIAN, have managed to calculate enthalpies and entropies of
the reactants, HA, HB, SA, and SB and the product, HC and SC, and the transition state, HTS
and STS. Write expressions for the equilibrium constant between A + B and C, and for the
reaction rate constant. Also, based on the available data, predict the activation energy and
pre-exponential factor in the Arrhenius expression for this reaction.
Match the following calculations with the best method for them. Each method can be
used only once. Give a very brief reason for each choice. [Note: While the highest-level
method could be a good choice for any of the calculations, there is one superior
combination when each method has to be used once.]
Calculation
Method
Average dipole moment of a water molecules
in solution
Hybrid QM/MM
Accurate atomization energy and heat of
formation of melamine
INDO/S
Geometric structure and frequencies of
a medium-size organometallic molecule
G3 ‘model chemistry’
Energy difference between different
conformers of a medium-size organic molecule
CCSD(T)/CBS
Epoxidation reaction mechanism of a small molecule
on the active site of chloroperoxidase
MD simulation
13
B3LYP
Barrier height in a small reaction system like
CH4 + H → CH3 + H2
MP2
Electronic excitation energies of Fe(CO)6
HF
C NMR chemical shifts for melamine