The merit of Boltztrap is that it can get the thermopower without the
relaxation time (tau)
[http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg05038.html],
but this is under the assumption that tau acts as an 'arbitrary'
constant [http://arxiv.org/abs/cond-mat/0602203v1].
The code can also give the electrical conductivity per relaxation time
(sigma/tau). However, if a calculated electrical conductivity (sigma)
is wanted, then an experimental tau or calculated tau is needed
[https://sites.google.com/site/cta4rbk/home/tips4vasp]. It is believed
that the experimental tau is more commonly used.
It seems that the latest version, Boltztrap V1.2.3, might be able to
estimate tau given the right input.
In the Boltztrap package (BoltzTraP_V1.2.3.tar.bz2)
[http://www.icams.de/content/departments/ams/madsen/boltztrap.html], the
following line can be seen in Table 1.1 of doc/UserGuide.pdf:
0 0 0 0 0 tau-model. Not documented
In the code (src/boseintegrals.F90), it appears that 'tau' might be the
variable 'lifetime' in Boltztrap.
It can be determined from the documented code (src/m_input.F90) that the
description of the parameters for the Table 1.1 line should be:
1 0 0 0 -1 #tau-model: tauref tauexp taurefen tempexp taureftemp
As seen in the line above, the default values if the line is not given
in case.intrans is:
tauref = 1
tauexp = 0
taurefen = 0
tempexp = 0 <= This value is not currently initialized with the other
parameters, so it might be uninitialized if the compiler does not set it 0.
taureftemp = -1
From the equation in the article Okuda et al. PRB 63 113104 (2001), it
can be seen that tau can be calculated if tauref, the energy (ene), and
tauexp are known.
tauref is the reference lifetime tau0 (femtoseconds)
[src/fermiintegrals.F90] <= Not sure why tauref in src/boseintegrals.F90
uses picoseconds
tauexp is the scattering parameter r (unitless) <= For r values, see
Durczewski et al. PRB 61 5303 (2000)
taurefen is the reference energy (Ry), e.g. Fermi level, at which tauref
is given
tempexp is the exponent for the temperature dependence (unitless) <= see
Table 1 of Asen-Palmer et al. PRB 56 9431 (1997)
-4 -> isotope effects phonon
-3 or -4 -> normal phonon
taureftemp is the reference temperature (K) for the given tauref
On 12/17/2013 4:10 AM, sonusha...@iitmandi.ac.in wrote:
Dear all
I want to know the value relaxation time τ, which is used as a
constant in the Boltztrap code.
Thanking you
Dr. Sonu Sharma
IIT Mandi (H.P.) India.
_______________________________________________
Wien mailing list
Wien@zeus.theochem.tuwien.ac.at
http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
SEARCH the MAILING-LIST at:
http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
