[CPMD-list] Reluctant hydrogen

[Erik Santiso]

Hi everybody. I've been dealing with a strange problem and I can't seem to find where the error is. I'm trying to do a wavefunction optimization for an isolated hydrogen atom using CPMD. I'm using a Vanderbilt pseudopotential and the HCTH functional, here's my input file:

&CPMD

 OPTIMIZE WAVEFUNCTION
 ISOLATED MOLECULE
 MEMORY BIG
 LSD

&END

&SYSTEM

SYMMETRY
 1
 CELL
 30.0000 1.0 1.0 0.0 0.0 0.0
 CUTOFF
 35 

&END

&ATOMS
  
*001-H-ghct--leweb.uspp BINARY
 LMAX=S
 1 
 10.0000   0.000000   0.0000000
&END 

&DFT
 
  FUNCTIONAL HCTH 
  GC-CUTOFF
   5.D-5
 
&END

Now, for some reason the above doesn't converge. If I try a different method (e.g. PCG MINIMIZE) it converges but gives a total energy of circa -0.4, which is not right. Since I programmed the HCTH into Dr. Vanderbilt's code myself, I thought there might be an error in the pseudopotential, but I've checked it and compared it with the one in functionals.f in CPMD and they give identical results. I've tried running the same thing with other pseudopotentials and with a similar input file they converge extremely fast to about -0.5. 

There's another glitch: if I remove the LSD option from the above input, it converges very fast to an energy of about -0.46. Now the question is: shouldn't it converge to a lower value in the LSD run? I thought there was a problem with the LSD_HCTH routine in CPMD, but I couldn't find any error in it either. I'm now out of ideas on what could be wrong here, so if anyone can give me a hint on what may be failing here I'd appreciate it very much. I'm not attaching the pseudopotential file or the code I used to generate it to avoid cluttering up all your mailboxes, if anybody wants to look into it let me know and I'll send the files ASAP. Thanks a lot!

Erik.

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