[Pw_forum] Re: Pw_forum digest, Vol 1 #1031 - 1 msg

[Paolo Giannozzi]

On Friday 16 June 2006 08:22, aarti srirangarajan wrote:

> Also I could not find any info on how to fix the spin moments
> in INPUT_PW  file.

this is the documentation of the relevant variables (for LSDA), 
slightly modified wrt the official version (admittedly not a marvel 
of clarity).
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starting_magnetization(i)
               REAL
               starting spin polarization (values between -1 and 1)
               on atomic type 'i' in a spin-polarized calculation.
               Breaks the symmetry and provides a starting point for
               self-consistency. The default value is zero, BUT a value
               MUST be specified for AT LEAST one atomic type in spin
               polarized calculations. Note that if start from zero
               initial magnetization, you will get zero final magnetization
               in any case. If you desire to start from an antiferromagnetic
               state, you may need to define two different atomic species
               corresponding to sublattices of the same atomic type.
               If you fix the magnetization with "nelup/neldw" or with
               "multiplicity" or with "tot_magnetization", you should
               not specify starting_magnetization
nelup, neldw   REAL
               number of spin-up and spin-down electrons, respectively
               Note that this fixes the final value of the magnetization.
               The sum must yield nelec that must also be specified
               explicitly in this case. Not valid for spin-unpolarized
               or noncollinear calculations, only for LSDA. Obsolescent:
               use multiplicity or tot_magnetization instead.

multiplicity   INTEGER ( default = 0 [unspecified] )
               spin multiplicity (2s+1). 1 is singlet, 2 for doublet etc.
               Note that this fixes the final value of the magnetization.
               if unspecified or a non-zero value is specified in nelup/neldw
               then multiplicity variable is ignored.
               Do not specify both multiplicity and tot_magnetization.

tot_magnetization INTEGER ( default = -1 [unspecified] )
               majority spin - minority spin (nelup - neldw).
               if unspecified or a non-zero value is specified in nelup/neldw
               then tot_magnetization variable is ignored.
               Do not specify both multiplicity and tot_magnetization.
               YES, there is redundancy! nelup/neldw are enough to specify
               the spin state. However these variables are not very convenient
               and will be eliminated from the input in future versions.
               It is recommended to use either 'multiplicity' or equivalently
               'tot_magnetization' to specify the spin state.
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-- 
Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy