Dear all,

I performed a DMFT calculation and use OmegaMaxEnt to obtain the corresponding

spectra, but I always get this error message:

"G(tau) must not change sign."

while using OmegaMaxEnt. What's the reason for this error? Is it because my DMFT

calculation doesn't converge well? How can I solve this issue?

Thanks!

## "G(tau) must not change sign" in DMFT calculation

### Re: "G(tau) must not change sign" in DMFT calculation

Dear,

It seems that your imaginary time Green's function changes sign which is not physically correct. Could you post a plot of your Green's function

in imaginary time (or the raw data) ?

Is your DMFT calculation correctly converged ?

Thanks

Bernard

PS: Could you precise your affiliation ?

Thanks

It seems that your imaginary time Green's function changes sign which is not physically correct. Could you post a plot of your Green's function

in imaginary time (or the raw data) ?

Is your DMFT calculation correctly converged ?

Thanks

Bernard

PS: Could you precise your affiliation ?

Thanks

Bernard Amadon

CEA

France

CEA

France

### Re: "G(tau) must not change sign" in DMFT calculation

Hello,

The DMFT calculation is hard to converge, so I only set a rather low criterion (tolvrs 1e-2) to perform

the calculation otherwise it could never finish. Do you think it is the main reason to make the sign

problem? (I set dmft_tollc=1e-5, but usually, it is not easy to achieve within a reasonable dmft_iter)

I took a look on your lecture http://ftp.abinit.org/ws11/Amadon.pdf and it looks possible to just make a

one shot DMFT calculation and a roughly picture can be obtained. If one-shot calculation is possible,

I suppose the convergence is not reached. If so, is convergence a critical issue that make the sign problem?

* Also a quick question:

Currently the dmft solver seems not support SOC case due to the spinor wavefunctions. If so,

do you think DMFT calculation reliable for 4f electrons? (I saw in your lecture, Ce2O3 works well

abinit DMFT calculation. As far as I know, Ce also has SOC. So do you think SOC effect important

in DMFT?)

Attached is a calculation for Eu metal where there is only one atom per unitcell, so should be a

rather simple case. Beacuse this is just a quick check, many parameters are not taken

to ensure high precision. Any suggestion to help me perform DMFT using abinit is appreciated !

Thanks!

Shu-Ting Pi

University of California, Davis

==================================================================

# << Project: Eu-LDA+DMFT >>

AUTOPARAL 1

ndtset 1 # how many running data set

jdtset 2

pawprtvol 3 # show more information

#Definition of the Structure ======================

chkprim 0 # check primitive cell, default: 1 (stop) / 0 (warn)

nsym 0 # number of symmetry, default: 0 (autocheck) / 1 (nosymm)

acell 3*4.018 angstrom # equal to 1 angstrom

angdeg 3*109.471 # angle betwee two basis vectors

ntypat 1 # Total types of atoms

znucl 63 # atom species (.files must in same order)

natom 1 # total atoms per unitcell

typat 1 # atom types

xred

0.0 0.0 0.0

# Spin-orbit =======================================

nspinor 1 # spinor

nspden 2 # spin density

nsppol 2 # spin polarizaton

spinat 0 0 0 # initial moments

pawspnorb 0 # turn on paw SOC

spnorbscl 1.0 # scaling of SOC

# Correlated Orbital ================================

usepawu 1 # Full localized doubling counting

dmatpuopt 1 # The density matrix: the simplest expression.

lpawu 3 # f-orb

#Convergence ==========================

ecut 14.7 # Maximal kinetic energy cut-off, in Hartree

pawecutdg 40 # ecut for paw double grid

occopt 3 # smearing of the energy levels

tsmear 1200 K

diemac 1.0e+6 # large value for metal

nband 40

# k-mesh ===========================================

kptopt 4 # kpt generation, if SOC, no TRS allowed

ngkpt 10 10 10 # k-mesh along each axis

nshiftk 1 # how many k-shift

shiftk # shift vector

0.5 0.5 0.5

istwfk *1

# DFT SCF ===========================================

nstep1 300 # Maximal number of SCF cycles

#nline1 10

#nnsclo1 10

upawu1 0.0 eV # U

jpawu1 0.0 eV # J

tolvrs1 1.0d-3

# DMFT ==============================================

usedmft2 1

nline2 20

nnsclo2 20

getwfk2 1

nstep2 100

tolvrs2 1.0d-2

upawu2 8.0 eV

jpawu2 1.0 eV

dmft_solv2 5 # CTQMC

dmftbandi2 6 # initial band

dmftbandf2 12 # final band

dmft_iter2 50

dmft_mxsf2 0.3

dmft_tollc 1e-5

dmft_dc2 1

dmft_nwlo2 100

dmft_nwli2 100000

dmftqmc_l2 50

dmftqmc_n2 1.d6

dmftqmc_therm2 10000 #10000

dmftctqmc_gmove2 0

dmftctqmc_order2 50 #50

The DMFT calculation is hard to converge, so I only set a rather low criterion (tolvrs 1e-2) to perform

the calculation otherwise it could never finish. Do you think it is the main reason to make the sign

problem? (I set dmft_tollc=1e-5, but usually, it is not easy to achieve within a reasonable dmft_iter)

I took a look on your lecture http://ftp.abinit.org/ws11/Amadon.pdf and it looks possible to just make a

one shot DMFT calculation and a roughly picture can be obtained. If one-shot calculation is possible,

I suppose the convergence is not reached. If so, is convergence a critical issue that make the sign problem?

* Also a quick question:

Currently the dmft solver seems not support SOC case due to the spinor wavefunctions. If so,

do you think DMFT calculation reliable for 4f electrons? (I saw in your lecture, Ce2O3 works well

abinit DMFT calculation. As far as I know, Ce also has SOC. So do you think SOC effect important

in DMFT?)

Attached is a calculation for Eu metal where there is only one atom per unitcell, so should be a

rather simple case. Beacuse this is just a quick check, many parameters are not taken

to ensure high precision. Any suggestion to help me perform DMFT using abinit is appreciated !

Thanks!

Shu-Ting Pi

University of California, Davis

==================================================================

# << Project: Eu-LDA+DMFT >>

AUTOPARAL 1

ndtset 1 # how many running data set

jdtset 2

pawprtvol 3 # show more information

#Definition of the Structure ======================

chkprim 0 # check primitive cell, default: 1 (stop) / 0 (warn)

nsym 0 # number of symmetry, default: 0 (autocheck) / 1 (nosymm)

acell 3*4.018 angstrom # equal to 1 angstrom

angdeg 3*109.471 # angle betwee two basis vectors

ntypat 1 # Total types of atoms

znucl 63 # atom species (.files must in same order)

natom 1 # total atoms per unitcell

typat 1 # atom types

xred

0.0 0.0 0.0

# Spin-orbit =======================================

nspinor 1 # spinor

nspden 2 # spin density

nsppol 2 # spin polarizaton

spinat 0 0 0 # initial moments

pawspnorb 0 # turn on paw SOC

spnorbscl 1.0 # scaling of SOC

# Correlated Orbital ================================

usepawu 1 # Full localized doubling counting

dmatpuopt 1 # The density matrix: the simplest expression.

lpawu 3 # f-orb

#Convergence ==========================

ecut 14.7 # Maximal kinetic energy cut-off, in Hartree

pawecutdg 40 # ecut for paw double grid

occopt 3 # smearing of the energy levels

tsmear 1200 K

diemac 1.0e+6 # large value for metal

nband 40

# k-mesh ===========================================

kptopt 4 # kpt generation, if SOC, no TRS allowed

ngkpt 10 10 10 # k-mesh along each axis

nshiftk 1 # how many k-shift

shiftk # shift vector

0.5 0.5 0.5

istwfk *1

# DFT SCF ===========================================

nstep1 300 # Maximal number of SCF cycles

#nline1 10

#nnsclo1 10

upawu1 0.0 eV # U

jpawu1 0.0 eV # J

tolvrs1 1.0d-3

# DMFT ==============================================

usedmft2 1

nline2 20

nnsclo2 20

getwfk2 1

nstep2 100

tolvrs2 1.0d-2

upawu2 8.0 eV

jpawu2 1.0 eV

dmft_solv2 5 # CTQMC

dmftbandi2 6 # initial band

dmftbandf2 12 # final band

dmft_iter2 50

dmft_mxsf2 0.3

dmft_tollc 1e-5

dmft_dc2 1

dmft_nwlo2 100

dmft_nwli2 100000

dmftqmc_l2 50

dmftqmc_n2 1.d6

dmftqmc_therm2 10000 #10000

dmftctqmc_gmove2 0

dmftctqmc_order2 50 #50

### Re: "G(tau) must not change sign" in DMFT calculation

Hello,

More generally, if you want more precise data, the first thing to do is to increase dmftqmc_n, which is rather low.

Could you please post your Green's function in imaginary time ?

Thanks

Bernard

More generally, if you want more precise data, the first thing to do is to increase dmftqmc_n, which is rather low.

Could you please post your Green's function in imaginary time ?

Thanks

Bernard

Bernard Amadon

CEA

France

CEA

France

### Re: "G(tau) must not change sign" in DMFT calculation

Hello Bernard,

I'm new to DMFT in abinit. The are many output files, which one are you talking about?

I got the following files with different names:

DS2_atom_01_Gtau_xx.dat

DS2_atom_01_Gw_xx.dat

DS2_atom__G0w_.dat

Gtau.dat

DS2Self-omega_iatom0001_isppol1

DS2Self-omega_iatom0001_isppol2

I can't find any document explain their meaning. Which file contains the GF in imaginary time?

(I guess, Gtau.dat? but which column? It's hard the understand the output of the dmft calculation).

Thanks!

--

Shu-Ting Pi

Postdoctoral Fellow

University of California, Davis

I'm new to DMFT in abinit. The are many output files, which one are you talking about?

I got the following files with different names:

DS2_atom_01_Gtau_xx.dat

DS2_atom_01_Gw_xx.dat

DS2_atom__G0w_.dat

Gtau.dat

DS2Self-omega_iatom0001_isppol1

DS2Self-omega_iatom0001_isppol2

I can't find any document explain their meaning. Which file contains the GF in imaginary time?

(I guess, Gtau.dat? but which column? It's hard the understand the output of the dmft calculation).

Thanks!

--

Shu-Ting Pi

Postdoctoral Fellow

University of California, Davis