Computational

Question 1

Which model is most suitable for TM?

Answer 1

B3LYP/6-31G*

Question 2

Which model is most suitable for unsaturated organics?

Answer 2

MP2/6-31G* or B3LYP/6-31G*

Question 2

Which model is most suitable for weakly associated dimers?

Answer 2

HF/G-311+G*

Question 3

Which model is most suitable for compounds with electronegative elements or lone pairs?

Answer 3

MP2/6-311+G*

Question 4

MM

How are electrons treated?

Answer 4

They are ignored

Question 5

Advantages of MM?

2 points

Answer 5

1. Quick not computationally demanding
2. Applicable to very large systems

Question 6

Disadvantages of MM?

4 points

Answer 6

1. Electrons are ignored
2. Bond energies, molecular orbitals, electron densities, excited states are not calculated
3. Primary function of force field is structure optimisation
4. Calculations depend on the force field used.

Question 7

Describe MD calculations

Answer 7

1. Take forces calculated on atoms
2. Apply Newton 2nd Law
3. Define time step
4. Output molecular trajectory

Question 8

MD

What is a typical time step?

Answer 8

1 fs

Question 9

MD

What do force fields define?

Answer 9

Potential energy surface

Question 10

MD

How are force fields calculated?

Answer 10

From the gradient of the potential energy surface

Question 11

What is the principle of Ab initio calculation?

Answer 11

MO theory approach to finding solutions to Schrödinger’s equation

Question 12

Ab initio

How are electrons treated?

Answer 12

Explicitly

Question 13

Ab initio

What does Hamiltonian operator describe?

Answer 13

KE & PE terms of matter

Question 14

Ab inito

How is the Hamiltonian operator approximated?

Answer 14

Using a level of theory Hartree-Fock or DFT

Question 15

Schrödinger equation

What is E?

Answer 15

Proportionality constant (the Eigenvalue)

Question 16

Schrödinger equation

What does the wavefunction describe?

Answer 16

Size and shapes of atomic and molecular orbitals

Question 17

Schrödinger equation

How is the wavefunction approximated?

Answer 17

Using a basis set. Linear combination of simple functions like Gaussian

Question 18

Born-Oppenheimer approximation of Hamiltonian operator

What happens to KE of electron

Answer 18

Worked out

Question 19

Born-Oppenheimer approximation of Hamiltonian operator

What happens to KE of nucleus

Answer 19

=0, as molecule is fixed in space for geometry optimisation

Question 20

Born-Oppenheimer approximation of Hamiltonian operator

What hapens to PE of electron to electon

Answer 20

Worked out

Question 21

Born-Oppenheimer approximation of Hamiltonian operator

What happens to PE of nucleus to nucleus

Answer 21

Calculated using Coulomb’s law

Question 22

Born-Oppenheimer approximation of Hamiltonian operator

What happens to PE of nucleus to electron

Answer 22

Calculated

Question 23

Which level(s) of theory approximate electron to electron correlation

Answer 23

DFT, Hybrid DFT

Question 24

Which level(s) of theory **ignore** electron to electron **correlation**

Answer 24

HF theory

Question 25

Which level(s) of theory **approximate** electron to electron **exchange**

Answer 25

DFT

Question 26

Which level(s) of theory **get exact** electron to electron **exchange**

Answer 26

HF theory, Hydrid DFT

Question 27

Describe Hartree theory

Answer 27

Replaces the insolvable many electron problem with the solvable single electron problem. Each electron modelled as a moving in an effective uniform field

Question 28

What is the disadvantage of HF theory

Answer 28

Missing electron correlation energy

Question 29

For what molecules is the missing electron correlation energy significant?

Answer 29

Significant for molecules with high electron density (aromatics)

Question 30

How many variable s per electron are used in HF?

Answer 30

4 | 3 positional + spin

Question 31

# Variation theorem Define **basis set**

Answer 31

Collection of Gaussian functions

Question 32

# Variaiton theorem Define **polarisation function**

Answer 32

One higher angular momentum function

Question 33

# Variation theorem Describe the process of variation theorem

Answer 33

1. Generate a trial wavefunction based on random weighting coefficients 2. Determine its energy 3. Vary weighting coefficients to get a new wavefunction. Is the new energy lower? 4. Repeat until the electronic ground state (minimum is found)

Question 34

# Basis sets What is the meaning of **dash**?

Answer 34

Treat core electrons separate from valence electrons

Question 35

# Basis sets What is the meaning of **star**?

Answer 35

Polarisation function (two stars — polarisation on the hydrogen as well as heavy; one star — only heavy, not hydrogen)

Question 36

# Basis sets What is the meaning of **plus**?

Answer 36

Diffuse function. Larger versions of ‘s’ and ‘p’ orbitals. Important for atoms that carry extra charge

Question 37

What is the difference between **semi-empirical** calculations and ab initio?

Answer 37

1. Remove core electrons from calculations 2. Use minimal basis set 3. Zero differential overlap

Question 38

What is zero differential overlap?

Answer 38

Ovelap integral between many atoms assumed to be zero

Question 39

# MD What is to be calculated to get the nature of the stationary point on the potential energy surface?

Answer 39

Nedd to calculate 3N-6 force constant

Question 40

# MD, PES stationary points What makes a minimum?

Answer 40

If all 3N-6 vibrational frequencies are real numbers

Question 41

# MD, PES stationary points What makes a saddle point?

Answer 41

If one freq is imaginary and the rest are real, 1st order transition state

Question 42

What is the main difficulty in calculating NMR with DFT?

Answer 42

Need specially constructued split-valence basis sets with enhanced descriptors for core electrons

Question 43

What can calculating EPR with DFT show?

Answer 43

By comparing plots from experimental you can verify the model and then assume that the molecular orbitals are shown correctly

Question 44

Electron correlation

Answer 44

Describes how the electric field/movement of one electron is influenced by the electric field/movement of all other electrons. It’s a manifestation of the many-body effect.

Question 45

Electron exchange

Answer 45

Describes the energy lowering obtained when spin up (alpha) electrons pair upwith spin down (beta) electrons