<div dir="ltr">Dear Gabriele,<div><br></div><div>To add to Paresh's question is it possible (and does it make sense) to constrain the magnetisation of only a few atoms and not the others? While the target here seems to be atoms 3 and 4 the other atoms are being made to pay the price so to speak. </div>
<div><br></div><div>One option, in the present framework, is to constrain the values of magnetisation of all other atoms to their respective lambda=0 values. Could this speed up the convergence with lambda? </div><div><br>
</div><div>Thanks,</div><div>Vardha.</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Mar 4, 2014 at 7:18 PM, Gabriele Sclauzero <span dir="ltr"><<a href="mailto:gabriele.sclauzero@mat.ethz.ch" target="_blank">gabriele.sclauzero@mat.ethz.ch</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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What about the evolution of the constrained magnetization?<br>
(Please also make sure that the values specified in
starting_magnetization make sense, as suggested by L. Paulatto
Sir).<br>
<br>
My suggestion was to vary lambda in small steps (say 0.5). I'm
surprised that you managed to converge the calculation with such
high lambda values.<br>
<br>
Anyway, the constrain energy looks way too large, your system is
probably still far from the target.<br>
<br>
<br>
GS<div><div class="h5"><br>
<br>
On 03/04/2014 01:57 PM, paresh rout wrote:<br>
</div></div></div><div><div class="h5">
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<div>Respected Sclauzero sir,<br>
</div>
Thanks for your reply. According to your suggestion, I
varied my Lambda value from 0,5,.......150 ry. Although
calculated constrained energy are decreasing but upto 150 ry
the constrained energy and the estimated scf accuracy are not
the same order. Here I am providing my constrained energy with
various lambda value.<br>
<br>
</div>
Lambda Constraint_Energy<br>
0 0.00000000<br>
5 36.93411685<br>
10 69.54815816 <br>
15 6.65653915 estimated scf accuracy <
7.6E-13 Ry<br>
20 7.88546052<br>
25 8.88385707<br>
30 9.71513061 <br>
35 10.42697250<br>
40 11.05006563<br>
45 11.60072229<br>
50 12.08887057<br>
70 13.54966033<br>
80 14.05546257<br>
90 14.45159513<br>
100 14.75974550<br>
110 14.99680383<br>
120 15.17624003<br>
130 15.30876396 <br>
140 15.40310437 estimated scf accuracy
< 9.9E-13 Ry <br>
150 15.46632278 estimated scf accuracy
< 9.9E-13 Ry<br>
<br>
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<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Tue, Mar 4, 2014 at 3:06 PM,
Sclauzero Gabriele <span dir="ltr"><<a href="mailto:gabriele.sclauzero@mat.ethz.ch" target="_blank">gabriele.sclauzero@mat.ethz.ch</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear
Paresh,<br>
<br>
in my understanding you should start with a very small
lambda value (e.g. 0.1), make sure the calculation has
converged (not always trivial), then restart with a larger
value.<br>
It is important to tune the steps by which you increase
lambda. Increasing it by steps of 5 seems too much to me, I
would suggest you to try much smaller steps, say between 0.1
and 0.5.<br>
<br>
There are two reasons why the energy increases: the first is
because you are constraining your system out of its ground
state, but that's exactly what one would expect. The other
is the contribution from the penalty energy (E_constrain, it
should be printed after each scf step), which is used to
impose the constraint.<br>
An important thing is that this energy term is not physical
and becomes negligible once your system reaches the target
state.Therefore one should monitor this constraint energy,
together with the constrained quantity, and make sure it
goes to zero at some point.<br>
<br>
Once lambda is large enough and you reached the targeted
state, E_constrain should be negligible w.r.t. the total
energy and of the same order of the estimated scf accuracy.
From that point on, the energy should not change if you
further increase lambda, because your system fulfills
(almost) exactly the constraint, so that E_constrain should
stay to a very low value.<br>
<br>
HTH<br>
<br>
<br>
GS<br>
<div><br>
Respected Lorenzo sir,<br>
Thanks for your replay but my question was
how to fix the proper LAMBDA value for any constrained
system as the energy is increasing with increase in lambda
value.Please suggest me something regarding lambda.<br>
<br>
<br>
<br>
</div>
<div>
<div>On Mon, Mar 3, 2014 at 5:54 PM, Lorenzo
Paulatto <<a href="mailto:lorenzo.paulatto@impmc.upmc.fr" target="_blank">lorenzo.paulatto@impmc.upmc.fr</a><mailto:<a href="mailto:lorenzo.paulatto@impmc.upmc.fr" target="_blank">lorenzo.paulatto@impmc.upmc.fr</a>>>
wrote:<br>
On 03/03/2014 12:39 PM, paresh rout wrote:<br>
Dear all,<br>
I am doing spin polarized calculations on a
multiferroic compound . In some cases I am doing
constrained magnetic calculations to get the Low-spin
and High-spin state . For this I am using<br>
constrained_magnetization='atomic'<br>
starting_magnetization(1) = 5.0<br>
starting_magnetization(2) = -3.0<br>
starting_magnetization(3) = 0.0<br>
starting_magnetization(4) = 0.0<br>
lambda =0,5,10,20,25,........etc<br>
<br>
<br>
<br>
+--------------------------------------------------------------------<br>
Variable: starting_magnetization(i), i=1,ntyp<br>
<br>
Type: REAL<br>
Description: starting spin polarization on atomic
type 'i' in a spin<br>
polarized calculation. Values range
between -1 (all spins<br>
down for the valence electrons of
atom type 'i') to 1<br>
(all spins up). Breaks the symmetry
and provides a starting<br>
point for self-consistency. The
default value is zero, BUT a<br>
value MUST be specified for AT LEAST
one atomic type in spin<br>
polarized calculations, unless you
constrain the magnetization<br>
(see "tot_magnetization" and
"constrained_magnetization").<br>
Note that if you start from zero
initial magnetization, you<br>
will invariably end up in a
nonmagnetic (zero magnetization)<br>
state. If you want to start from an
antiferromagnetic state,<br>
you may need to define two different
atomic species<br>
corresponding to sublattices of the
same atomic type.<br>
starting_magnetization is ignored if
you are performing a<br>
non-scf calculation, if you are
restarting from a previous<br>
run, or restarting from an
interrupted run.<br>
If you fix the magnetization with
"tot_magnetization",<br>
you should not specify
starting_magnetization.<br>
+--------------------------------------------------------------------<br>
<br>
<br>
kind regards<br>
<br>
<br>
--<br>
Dr. Lorenzo Paulatto<br>
IdR @ IMPMC -- CNRS & Université Paris 6<br>
phone:+33 (0)1 44275 084 / skype: paulatz<br>
www: <a href="http://www-int.impmc.upmc.fr/%7Epaulatto/" target="_blank">http://www-int.impmc.upmc.fr/~paulatto/</a><br>
mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu
75252 Paris Cédex 5<br>
</div>
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