Computational Chemistry Exam latest for 2024/ Computational Chemistry Exam
latest for 2024/ ACS CHEMISTRY GENERAL EXAM COMBINED
Plastic Molecular Models - ANSWER-Fixed bond lengths and coordination
geometries
Provide 3D structure
No information on properties, energetics, or reactivity
Semi-Empirical Molecular Orbital Methods - ANSWER-Approximate descriptions
of valence electrons
Obtained by solving simplified form of Schrodinger equation
Integrals are approximated with empirical expressions
Semi-quantitative description of electronic distribution, molecular structure,
properties, and relative energies
Ab Inito Molecular Orbital Methods - ANSWER-More accurate treatment of
electronic distribution using the full Schrodinger equation
Systematically improved to obtain chemical accuracy
Does not need to be parametrized or calibrated with respect to the experiment
Describes structure, properties, energetics, and reactivity
Hartree-Fock Wavefunction - ANSWER-Treats each electron independently
Neglect electron electron correlation
Solves one electron properties
A many electron wavefunction approximated by a product of one electron
orbitals
,Population Analysis - ANSWER-Divide up the total electron density into
contributions from the individual atoms or basic function
Each orbital is normalized
In a closed shell molecule, each occupied orbital contains 2 electrons
Each orbital is a linear combination of basis functions
Plug into the expression for the total number of electrons and rearrange the
terms
Charges from Electrostatic Potentials - ANSWER-Charges from a least square to
the electrostatic potential
What is the dipole moment for HF and DFT calculations? - ANSWER-The
expectation value of the classical expression for the dipole - can be written in
terms of the density matrix and a set of dipole integrals over a basis function
What is the dipole moment for MPn, CI, and CC calculations? - ANSWER-The
derivative of the energy with respect to the applied field - need to calculate the
derivative of the density to get the relaxed or response density
First order properties - ANSWER-Expressed as first derivative of the energy
Dipole and higher multipole moments
Electric field and electric field gradient
ERP - hyper fine coupling constants
Second order and higher properties - ANSWER-Requires second and higher
derivatives of the energy
Polarizability and hyperpolarizability
,Force constants, vibrational frequencies and intensities
Magnetic susceptibility and NMR shielding
VCD and ROA
Potential Energy Surfaces (PES) - ANSWER-Displays the energy of a molecule as a
function of its geometry
What is the vertical axis of PES? - ANSWER-Energy
What is the horizontal axis of PES? - ANSWER-Geometric coordinates
What does the equilibrium molecular structure correspond to on a PES? -
ANSWER-The minima in the valleys
How are energetics of reactions calculated from a PES? - ANSWER-From the
energies or altitudes of the minima for reactants and products
What is a reaction path in PES? - ANSWER-A path that connects reactants and
products through a mountain pass
Where is the transition structure on a PES? - ANSWER-The highest point on the
lowest energy path
How are reaction rates obtained from a PES? - ANSWER-The height and profile
of the potential energy surface around the transition structure
, What determines the vibrational spectrum in a PES? - ANSWER-The shape of the
valley around the minimum
How is the electronic spectrum obtained from a PES? - ANSWER-The separation
between the separate potential energy surfaces of each electronic state
What properties are given from a PES? - ANSWER-Dipole moment
Polarizability
NMR shielding
What approximation is used for PES? - ANSWER-The Born-Oppenheimer
approximation
What are the similarities of DFT and HF? - ANSWER-Use Born-Oppenheimer
Optimizes coefficients of orthogonal spin
Coefficients found in an iterative procedure
Need a basis sets
Can use RHF, UHF
What are the differences of DFT and HF? - ANSWER-DFT uses electron density,
HF uses one electron wavefunctions
DFT uses principle exact
HF uses insert limitations
Exchange and Correlation not defined in same way
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