Van del waals interaction in qm

In summary, Van der Waals interaction, also known as London dispersion force, is a quantum mechanical phenomenon that occurs between molecules due to temporary fluctuations in electron distribution. It plays a crucial role in determining the physical and chemical properties of molecules, affecting their boiling and melting points, surface tension, viscosity, and stability. This interaction can be both attractive and repulsive, with its strength decreasing as the distance between molecules increases. It is present in everyday life, contributing to cohesive forces between water molecules and adhesion between gecko feet and surfaces.
  • #1
alejandrito29
150
0
Hello

I read the follow paper about van del waals interaction in quantum mechanics

http://www.damtp.cam.ac.uk/user/gold/pdfs/teaching/van_der_waals.pdf

In this paper the potential

[tex]V= e^2/R + e^2/(R+y)+e^2/(R-x)+ e^2/(R+y-x) [/tex]

is aproximated to [tex]V \approx -2 e^2/R^3 xy[/tex]

with R>>|x|,|y|

why this paper use this aproximation?

if i use Taylor series, my aproximation is

[tex]V=4 e^2 /R + 2 e^2/R (x-y) + 2 e^2 /R^3 (x^2+y^2) -2 e^2/R^3 xy[/tex]
 
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  • #2
ohh, sorry, my problem is with signus of V...delete my post please
 

1. What is Van der Waals interaction in quantum mechanics?

Van der Waals interaction, also known as London dispersion force, is a weak intermolecular force that occurs between molecules due to temporary fluctuations in electron distribution. It is a quantum mechanical phenomenon that arises from the interaction of fluctuating dipole moments in molecules.

2. How does Van der Waals interaction affect molecular properties?

Van der Waals interaction plays a crucial role in determining the physical and chemical properties of molecules. It affects the boiling and melting points, as well as the surface tension and viscosity of substances. It also contributes to the stability of molecular structures.

3. Can Van der Waals interaction be attractive and repulsive?

Yes, Van der Waals interaction can be both attractive and repulsive. At short distances, the interaction is repulsive as the electron clouds of molecules start to overlap. However, at longer distances, the interaction becomes attractive, leading to the formation of weak bonds between molecules.

4. How does the strength of Van der Waals interaction vary with distance?

The strength of Van der Waals interaction decreases as the distance between molecules increases. This is because the attractive force between molecules is inversely proportional to the sixth power of the distance. Thus, the interaction becomes weaker as the distance increases.

5. Can Van der Waals interaction be observed in everyday life?

Yes, Van der Waals interaction is present in everyday life. It is responsible for the cohesive forces between water molecules, which allow insects to walk on water. It also contributes to the adhesion between gecko feet and surfaces, allowing them to climb on vertical walls.

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