i use qe to calculate the bands of mgb2 ,and get a semiconductor result with gap.but from the paper i know it is a superconductor, i dont know whats wrong with the parameter i choose?
&control
calculation = 'scf'
restart_mode='from_scratch',
prefix='mgb2',
tstress = .true.
tprnfor = .true.
pseudo_dir = '****/qe-6.1/pseudo/',
outdir='*****/tempdir/'
/
&system
ibrav= 4, celldm(1) =5.826027964, celldm(3)=1.142 nat= 3, ntyp= 2,
nbnd =6,
ecutwfc =30.0,
ecutrho = 72,
occupations='smearing',
degauss=0.01,
smearing='mv'
/
&electrons
diagonalization='david'
mixing_mode = 'plain'
mixing_beta = 0.7
conv_thr = 1.0d-8
/
ATOMIC_SPECIES
mg 24.305 Mg.pz-n-vbc.UPF
b 10.811 B.pz-vbc.UPF
ATOMIC_POSITIONS {crystal}
mg 0.000000 0.000000 0.000000
b 0.333333 0.666667 0.500000
b 0.666667 0.333333 0.500000
K_POINTS {automatic}
24 24 24 0 0 0
thanx
with 2 gaps is still a superconductor ? what does it mean ? and how to set the parameters?
thanx
You do not specify what formalism you are employing, however in general in order to establish whether one has a superconducting gap one will have to deal with a formalism that explicitly takes account of the anomalous Green function. A non-vanishing anomalous Green function signifies superconductive paring and a non-vanishing superconducting gap (which may be dispersive and vanishing in certain regions of the k space). For details, you may wish to consult the microscopic BCS theory as described, for instance, in Chapter 13, Sec. 51 (beginning on page 439) of the book Quantum Theory of Many-Particle Systems, by AL Fetter and JD Walecka (Dover, New York, 2003). Incidentally, gap is not necessary for superconductivity, as discussed by S Weinberg in the attached publication (Superconduetivity for Particular Theorist, Prog.Theor. Phys. Suppl., No. 86, pp. 43-53 (1986)).
http://ci.nii.ac.jp/els/110001208319.pdf?id=ART0001546076&type=pdf&lang=en&host=cinii&order_no=&ppv_type=0&lang_sw=&no=1490317005&cp=
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