<div>Dear Dan,</div><div><br></div>I have seen this error in several cases particularly for transition metals and<div>for basis and projector functions generated by our atompaw program. My understanding</div><div>(based on a discussion with Stefano de Gironcoli) is that the program stops when the</div>
<div>program detects a certain product of one-center terms to be negative. In my experience</div><div>these terms can be negative before convergence and I have commented out the offending </div><div>line. In my tests, this allows the program to converge consistently in the tests I have done.</div>
<div>This is not necessarily safe or well-tested and I did promise to look into it further. In case</div><div>you would like to also try, the offending line in 4.2.1 is line 553 in sct_mod.f90:</div><div><br></div><div>
IF (okpaw) rho_ddot = rho_ddot + paw_ddot(rho1%bec, rho2%bec)</div><div><br></div><div>I repeat that commenting out this line may not be a good idea, but it has worked for me in</div><div>limited tests. (I still hope to do more tests.)</div>
<div>
<br></div><div> Sincerely,</div><div> Natalie Holzwarth</div><div>
<br></div><div><meta http-equiv="content-type" content="text/html; charset=utf-8">N. A. W. Holzwarth email: <a href="mailto:natalie@wfu.edu" target="_blank">natalie@wfu.edu</a><div>Department of Physics web: <a href="http://www.wfu.edu/~natalie" target="_blank">http://www.wfu.edu/~natalie</a></div>
<div>Wake Forest University phone: 1-336-758-5510 </div><div>Winston-Salem, NC 27109 USA office: Rm. 300 Olin Physical Lab</div>
<br><div class="gmail_quote">On Wed, Jul 6, 2011 at 5:54 AM, Dan Fors <span dir="ltr"><<a href="mailto:forsdan@gmail.com" target="_blank">forsdan@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Dear users,<br>
<br>
I am running a simple 2-atomic non-magnetic (NM) bcc Cr system (see<br>
below for the input file) with v.4.2.1 and I keep getting an error<br>
message regarding a negative dr2:<br>
<br>
from mix_rho : error # 1<br>
negative dr2<br>
<br>
This error occurs for values close to as well as away from the<br>
estimated equilibrium volume. What is the possible the origins of this<br>
error and how may I eliminate it?<br>
<br>
I have tried to change the mixing_beta in the range 0.1 to 0.8, as<br>
well as changing the mixing mode to 'TF'. I have also tried to set<br>
nspin = 2 with a zero start magnetisation since an anti-ferromagnetic<br>
(AFM) start configuration does not give rise to the problem (but<br>
yields the AFM solution instead of the NM one). However. this also<br>
gives the error. Finally, I tested to use ibrav = 3 and with only one<br>
atom in the cell, but I still get the above error.<br>
<br>
What I have noticed is that in the AFM case I get a couple of very<br>
flat bands in the bandstructure just above the Fermi level. If I<br>
change to a USPP potential or an alternative PAW potential these bands<br>
disappear, and the above error does not occur. Can the potential I use<br>
in the present case be the source to the error, and if yes, what is<br>
the reason behind it?<br>
<br>
I would appreciate any help or suggestions.<br>
<br>
Dan<br>
<br>
<br>
<br>
%-------------------------------------<br>
<br>
&CONTROL<br>
calculation = 'scf',<br>
restart_mode = 'from_scratch',<br>
prefix = 'Cr',<br>
tstress = .true.,<br>
tprnfor = .true.,<br>
pseudo_dir = '/home/forsdan/PROGRAMS/QUANTUM_ESPRESSO/espresso-4.2.1_intel/pseudo/',<br>
outdir = '/home/forsdan/FeCr_PROJECT/TEMP_PAW/'<br>
/<br>
&SYSTEM<br>
ibrav = 1, celldm(1) = 5.378798, nat = 2, ntyp = 1,<br>
ecutwfc = 40.0, ecutrho = 180.0, nbnd = 14<br>
occupations = 'smearing',<br>
smearing = 'mp', degauss = 0.022,<br>
nspin = 1,<br>
/<br>
&ELECTRONS<br>
electron_maxstep = 100,<br>
conv_thr = 1.0d-8,<br>
diagonalization = 'cg',<br>
mixing_mode = 'plain',<br>
mixing_beta = 0.3<br>
/<br>
ATOMIC_SPECIES<br>
Cr 51.996 Cr.pbe-paw_kj_6.UPF<br>
ATOMIC_POSITIONS {crystal}<br>
Cr 0.00 0.00 0.00<br>
Cr 0.50 0.50 0.50<br>
K_POINTS {automatic}<br>
12 12 12 0 0 0<br>
<br>
%-------------------------------------<br>
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</blockquote></div><br><br clear="all"><br><br><br>
</div>