[Pw_forum] Noncollinear magnetism

[W. YU]

Dear Pw users,

I have several questions about non collinear magnetism
calculation as shown in example13.

The following is quoted from the calculation for Fe
with penalty functional: 
-----------------------------------------------------
# self-consistent calculation with penalty functional
 &system
    ibrav = 3, celldm(1) =5.217, nat= 1, ntyp= 1,
    ecutwfc = 25.0,ecutrho = 200.0,
    report=1,
    occupations='smearing', smearing='gaussian',
degauss=0.05
    noncolin = .true.
    starting_magnetization(1) = 0.5
    angle1(1) = 90.0
    angle2(1) =  0.0
    mcons(1,1) = 0.0
    mcons(2,1) = 0.5
    mcons(3,1) = 0.0
    i_cons = 1
    lambda = 1
 /
=================================================
I have these questions:

1.From the input menu, I know the mcons(i,j) is the
i'th component of j'th atom type where i runs from 1
to 3. But if angle1(1)=90.0 and angle2(1)=0.0, the
magnetic moment should be along X axis, but the
constraint seems to leave the Y axis unchanged is 2
represents Y axis. It seems that 1,2 and 3 represent
Z, X and Y axses, am I right?
---------------------------------------------------
2. I hope to know how to choose lambda. why it is 1
here in the example.
===================================================
The following is quoted from the calcualtion fo Ni:

 # self-consistent calculation
cat > ni.scf.in << EOF
 &control
    calculation='scf'
    restart_mode='from_scratch',
    pseudo_dir = '$PSEUDO_DIR/',
    outdir='$TMP_DIR/'
    prefix='ni'
 /
 &system
    ibrav=2, celldm(1) =6.48, nat=1, ntyp=1,
    starting_magnetization(1)=0.7,
    ecutwfc = 24.0, ecutrho = 288.0,
    occupations='smearing',
smearing='methfessel-paxton', degauss=0.02
    noncolin = .true.
    starting_magnetization(1) = 0.1
    angle1(1) = 90.0
    angle2(1) =  0.0
 /
====================================================
3. Now the question is: Why there are two starting
manetisation when there is only one type of Ni atom?
4. On what basis do we choose smearing scheme such as
"methfessel-paxton" or "Gaussian"?
5. Last but most important question is: can we do
calculations on spiral? If the answer is positive, do
we have to use a very large supper cell? 
======================================================

Your answers and comments would be much a preciated.

W. YU

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