[molpro-user] DFT calculations produced different energy with a different guesses

[Kirk Peterson]

David,

it looks to me that you're getting stuck into a few local minima.  Do these different calculations converge to different structures?  How different are the energies at the starting geometries?  I would strongly recommend printing the orbitals and taking a careful look.   You could also try doing a CASSCF calculation (print the orbitals and CI vector)  to see how things should really be occupied.

regards,

Kirk


On Nov 3, 2010, at 6:19 AM, David Danovich wrote:

> Hello,
>  
> I am calculating CuAu2 molecule in high spin state (4B2 state) using B3LYP method. Below you can find three different possibilities I have used in the calculations. In the first one 1) I have calculated first HF wave function and used it as a guess for DFT calculation. Energy I got was -468.86467917 au. In the second calculation 2) I directly have calculated B3LYP without HF wave function. The energy I got was -468.83995914 au. In the third calculation 3) I first have done B3LYP calculation for state (4A2) and then used it as a guess for the calculations of 4B2. The energy I got was 
> -468.85824088 au. As you can see there is quite large difference in energy for the same state. I was trying to use different grids but it does not solved the problem. In my opinion result should not depend on the guess so drastically. What can be a solution for this problem?
> 
> Thank you in advance  David
>  
> 1)
> 
> ***, Peterson PP tz basis set
> memory,250,m
>  r =   2.72684681 ang;
>  a = 60.65125012 degree;
> geometry={Cu1;              !z-matrix geometry input
>           Au2,Cu1,r;
>           Au3,Cu1,r,Au2,a;
>           }
> basis=cc-pVTZ-PP
> 
> {hf,maxit=500;
> wf,57,3,3}
> 
> {rks,b3lyp3,maxit=500;
> wf,57,3,3}
> 
> optg
> 
> Total energy  -468.86467917 au
> ____________________________________________________
> 
> 2)
> ***, Peterson PP tz basis set 
> memory,250,m
>  r =   2.72684681 ang;
>  a = 60.65125012 degree;
> geometry={Cu1;              !z-matrix geometry input
>           Au2,Cu1,r;
>           Au3,Cu1,r,Au2,a;
>           }
> basis=cc-pVTZ-PP
> 
> {ks,b3lyp3,maxit=500;
> shift,-0.1,0.0;
> wf,57,3,3}
> 
> optg
> 
> Total energy -468.83995914 au
> 
> ______________________________________________________
> 
> 3)
> ***, Peterson PP tz basis set 
> memory,250,m
>  r =   2.72684681 ang;
>  a = 60.65125012 degree;
> geometry={Cu1;              !z-matrix geometry input
>           Au2,Cu1,r;
>           Au3,Cu1,r,Au2,a;
>           }
> 
> ! cc-pVTZ-PP
> 
> basis=cc-pVTZ-PP
> 
> {ks,b3lyp3,maxit=500;
> wf,57,4,3}
> 
> {ks,b3lyp3,maxit=500;
> shift,-1.0,0.0;
> wf,57,3,3}
> 
> optg
> 
> Total energy -468.85824088 au
> 
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