[Wien] Problem with energy difference GGA & LDA

[Jorissen Kevin]

Depends on your system !  The number of k-points seems to be rather large, I wouldn`t expect any problem there.  Try the same calculation (for both structures) using rkmax 8, and see whether your energy difference is the same (total energy for each structure probably isn`t, but energy differences normally converge faster than energies).  If you don`t trust your gmax, then do the same thing for gmax 16 or 18.
 
About the difference GGA/LDA : I`m not sure this is such a surprise.  You know, sometimes they even predict different ground states - luckily, this does not seem to be the case here.
Another thing to think about : maybe you optimized the structures for one of either functionals?
 
Kevin.
 

	-----Original Message----- 
	From: krutibas panda [mailto:krutibas at hotmail.com] 
	Sent: Fri 4/9/2004 9:40 AM 
	To: wien at zeus.theochem.tuwien.ac.at 
	Cc: 
	Subject: [Wien] Problem with energy difference GGA & LDA
	
	

	Dear Wien2k users,
	
	I have a compound orthorhombic (Pnma). I found the energy difference between
	the undeformed state and the deformed state using GGA. The energy diffrence
	i am getting is in about 0.0035 Rydbergs (~ 3 mRy). This difference seems
	right
	
	I did the same calculation using LDA, but the energy difference i am getting
	is kinda big , about 0.012 Rydbergs (~12 mRy).  The energy difference is
	kinda large.
	
	The above observation occurs with the same set of parameters (Rkmax = 7,
	Gmax=14) and with 5000 k points.
	
	Could someone tell me if i am doing anything wrong with my LDA calculation.
	Do i need to change any of those above mantioned parameters ?
	
	thanks in advance
	krutibas
	university of utah
	kpanda at mines.utah.edu
	
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