This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Hartree-Fock Self Consistent Field Method”.
1. What interactions are ignored in the Hartree-Fock calculations?
a) Proton-neutron interaction
b) Atom kinetic energy
c) Electron-nucleus attraction
d) Interelectron repulsion
View Answer
Explanation: If interelectron terms are ignored, the Schrodinger equation for n-electron atoms can be separated into n-hydrogen atoms. The approximate wavefunction is the product of n-hydrogen atom wavefunctions.
2. How are parameters in the Hartree-Fock method varied?
a) The variational function is a product of n orbitals
b) The variational function is an addition of n orbitals
c) The variational function is the sum of n orbitals
d) The variational function is just the hydrogen orbital wavefunction
View Answer
Explanation: The variational function Φ is a product of n orbitals that contain parameters to be evaluated by the variational method. Φ = g1(r1, θ1, Φ1) g2(r2, θ2, Φ2 )….gn(rn, θn, Φn). Each orbital is a product of a radial factor and spherical harmonic.
3. What is correlation energy?
a) Hartree-Fock energy approximated to the first degree
b) Difference between actual and Hartree-Fock energy
c) Actual energy
d) Successive orbital energy approximations
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Explanation: Correlational energy is the difference between actual and Hartree-Fock energy. This energy is large enough to cause a problem in calculations. It introduces larger error in calculation and differences in orders of electron volts are problematic.
4. How can the effects of instantaneous electron interaction be included?
a) It is too complex to include all electron-electron interactions
b) By excluding kinetic energy and just putting potential energy interactions
c) By including each interaction in the Hamiltonian
d) By including electron configurations in a trial wavefunction using variational approach
View Answer
Explanation: Including excited electronic configurations in a trial wavefunction, and this can be iterated using variational method. By including more configurations, the true wavefunction can be approached more closely. This method is not mathematically impossible but requires tedious iterations.
5. Which of the following happens when the atomic number (nuclear charge) of an element increases?
a) Energies of inner orbitals become more negative
b) Energies of inner orbitals become more positive
c) Energies of the inner orbitals remain unchanged
d) Energy spacings between orbitals increase
View Answer
Explanation: As atomic number increases, the energies of inner orbitals become more negative because of the increased attraction between the nucleus and electrons. Orbitals with lower probability densities have higher energies at specified positions. S orbitals close to the nucleus have low energy as they are not shielded by electrons.
Sanfoundry Global Education & Learning Series – Physical Chemistry.
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