# Stationary Points U(x,y): Periodicity & TS Barriers

For the TS barriers, you can consider the potential energy difference between two adjacent minima and use that to calculate the energy barrier. This would depend on the values of A and B in the equation. Possible analytical curves that could separate the basins of attraction of adjacent minima could be straight lines or curves that follow the shape of the potential function. In summary, the equation U(x,y)=Asin(pi*x/Lx) + Bcos(pi*y/Ly) has stationary points that can be found by differentiating and solving for zero, a periodicity that can be expressed in a single term, and possible analytical curves that could separate the basins of attraction of adjacent minima. The TS barriers for an atom diffusing on
U(x,y)=Asin(pi*x/Lx) + Bcos(pi*y/Ly) where A,B,Lx,Ly are positive

1 Locate all the stationary points (i.e. minima, maxima and transition states
(TS)) for this potential.

a. What is the periodicity of U(x,y) along the two directions?

b. Derive the TS barriers that an atom diffusing on the surface would
have to surmount during a “jump” between two minima as a function
of A and B.

c. Using information about the shape of U(x,y), propose possible
analytical curves separating the basin of attraction of adjacent minima.

I don't know about the TS barrier or separating the basin of attraction, but the stationary points can be found by differentiating the equation, equating it to zero and finding the solution. The solutions are the stationary points.

For the periodicity, you can express the above function in a single term which takes into account both the trigonometric functions, and find the periodicity of that.

## 1. What are stationary points in the context of U(x,y)?

Stationary points, also known as critical points, are points on a graph where the derivative is equal to zero. In the context of U(x,y), they represent points where the potential energy surface is either a maximum or minimum value.

## 2. How can I determine if a stationary point is a maximum or minimum?

To determine if a stationary point is a maximum or minimum, you can use the second derivative test. If the second derivative is positive, then the stationary point is a minimum. If the second derivative is negative, then the stationary point is a maximum. If the second derivative is zero, then the test is inconclusive and further analysis is needed.

## 3. What is periodicity and how does it relate to stationary points?

Periodicity refers to the repetition of a pattern over a specific interval. In the context of stationary points, periodicity can occur when the potential energy surface has multiple minima or maxima, resulting in a repeating pattern. This can be seen in systems with periodic boundary conditions, such as a crystal lattice.

## 4. What are TS barriers and why are they important in the study of stationary points?

TS (transition state) barriers are energy barriers that must be overcome for a system to transition from one stationary point to another. They are important in the study of stationary points because they provide insight into the stability and dynamics of a system. A high TS barrier indicates a more stable system, while a low barrier suggests a more dynamic and potentially unstable system.

## 5. How can I use stationary points and TS barriers in my research?

Stationary points and TS barriers can be used in various fields of research, such as chemistry, physics, and materials science. They can provide valuable information about the behavior and properties of a system, which can be used to make predictions and design experiments. They are also important in computational methods, such as density functional theory, for studying the electronic structure and reactions of molecules and materials.

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