Van del waals interaction in qm

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]
 
ohh, sorry, my problem is with signus of V....delete my post please
 

Related Threads for: Van del waals interaction in qm

  • Posted
Replies
1
Views
982
  • Posted
Replies
2
Views
2K
  • Posted
Replies
15
Views
7K
  • Posted
Replies
2
Views
2K
Replies
2
Views
651
  • Posted
Replies
1
Views
935
Replies
7
Views
2K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top