MChem Master of Chemistry Computational Chemistry 2

Question 1

In the ONIOM method, how is a large molecular system treated?

Accepted Answer

Divided into layers computed at different levels of theory

Answer

ONIOM partitions a molecule into layers, treating the reactive core at a high QM level and the surrounding environment at a lower MM or QM level.

Question 2

What does the potential energy surface (PES) represent in a chemical reaction?

Accepted Answer

Energy as a function of nuclear coordinates

Answer

The PES maps the total energy of a molecular system as a function of its nuclear coordinates, revealing minima, transition states, and reaction pathways.

Question 3

Which algorithm is most commonly used to locate transition states on a potential energy surface?

Accepted Answer

Nudged elastic band (NEB) or quasi-Newton eigenvector following

Answer

Methods like nudged elastic band and quasi-Newton eigenvector following locate saddle points (transition states) on the PES.

Question 4

In normal mode analysis, a transition state is characterized by how many imaginary vibrational frequencies?

Accepted Answer

Exactly one

Answer

A true transition state has exactly one imaginary vibrational frequency corresponding to motion along the reaction coordinate.

Question 5

What is the purpose of Ewald summation in periodic boundary condition simulations?

Accepted Answer

To efficiently compute long-range electrostatic interactions

Answer

Ewald summation splits the long-range Coulomb sum into rapidly converging real-space and reciprocal-space components for periodic systems.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Computational Chemistry 2