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Date: Thu, 09 Dec 2004 15:50:42 -0800
From: "Bylaska, Eric J" <Eric.Bylaska@pnl.gov>
Subject: RE: translational (a)symmetry in PSPW calculations
To: Lev Gelb <gelb@wuchem.wustl.edu>
Cc: nwchem-users@emsl.pnl.gov
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 Lev,

    How are you initializing the wavefunctions?
Try using

set nwpw:lcao_skip .true.

	
						Eric Bylaska

-----Original Message-----
From: owner-nwchem-developers@emsl.pnl.gov
[mailto:owner-nwchem-developers@emsl.pnl.gov] On Behalf Of Lev Gelb
Sent: Thursday, December 09, 2004 12:20 PM
To: nwchem-users@emsl.pnl.gov
Subject: translational (a)symmetry in PSPW calculations

In the following input deck, which does a PSPW calculation
on two lithium atoms at 5 angstrom separation, 
I'm finding the following strange behavior:

a) if the atoms are both placed on the box midline (relative coords): (
0.5, 0.5, Zvalue),  the reported energy is:  -0.4143363751E+00 Hartree,
and there is substantial spin-contamination of: <S^2>=0.873645199
(unrestricted calculation)

b) if the atoms are both placed on a different line:
( 0.25, 0.25, Zvalue), the reported energy is:  -0.4041411428E+00
Hartree, with basically zero spin-contamination. (unrestricted
calculation)

c) if the calculation is 'restricted', the both cases (a) and
(b) give exactly the same result, which is the "b" solution.

d) LDA calculations give the same result for (a) and (b).

This is a homolytic dissociation, so one might expect that
at large separations there is substantial multi-determinant character;
in fact, if I measure a potential-energy surface by scanning the bond
length, I find that in case (a) I get a surface that goes asymptotically
to zero bond energy, 
while in case (b) I get a RHF-like result with the bond energy becoming
significantly positive at large separations.

Since these are fully periodic calculations, why is it
that a simple translation within the unit cell gives these
two different limiting behaviors?   I have scanned over the
line connecting the two atoms, as well;  I get type (a) behavior from
(0.5, 0.5, Z) to (0.29, 0.29, Z), and then type (b) behavior from (0.28,
0.28, Z) to (0.0, 0.0, Z)

Running NWChem 4.6 on two processors of an AMD MP2200+, RH 9 OS.

Any advice would be appreciated!

# input file follows:

scratch_dir  ./working
permanent_dir  ./working
Start Lithium_dimer_E10
echo
memory 750 mb
charge 0

geometry units angstrom noautosym noautoz print
system crystal
lat_a 15.0000
lat_b 15.0000
lat_c 15.0000
alpha 90.0
beta 90.0
gamma 90.0
end
Li  0.50000000  0.50000000  0.20000000
Li  0.50000000  0.50000000  0.53333333
end

nwpw
pseudopotentials
  Li library library1
end
simulation_cell
ngrid 30 30 30 
end
unrestricted
xc pbe96
tolerances 1.0e-7 1.0e-8
ewald_ncut 3
end

set nwpw:psi_nolattice .true.
set nwpw:mimimizer 2

task pspw energy