Im(electron Self Energy)

[inoka]

Dear all

I am new to EPW and I need to calculate electron self energy of my sample. Thus I followed the diamond example. However I have some basic problems on using this code. Unfortunately I donot have any experienced users of EPW here in my uni. Thus I appreciate your support to do this calculation correctly.

01. I need to know whether the E(ibnd) in linewidth.elself file is wrt Fermi energy ( i.e whether the fermi energy is always zero in that file)

02. I repeated my calculation for different "fsthick" parameters and noticed it change linewidth.elself greatly. How I can choose the correct fsthick for my case, what is the criteria?

Thank you

[carla.verdi]

Dear inoka,

The energies printed in linewidth.elself are wrt to the Fermi energy.
The parameter fsthick will control the energy window around the Fermi level for which you want to calculate the linewidth, however near the boundaries of this window they won't be accurate. If this is the behavior you observe, then you can adjust fsthick depending on the needs of your calculation.

Best
Carla

[inoka]

Dear Carla

Thank you very much. I calculated Im(elself) for my system and plotted (E Vs Im(self)) the data in elself file to get the electron relaxation time. But I get two slightly separated parallel lines for my data. ( I copied my data below.) Thus I have two values at fermi energy as 26.4883 meV (at k-31) and/or 31.3564 meV (at k-188).

My questions are:
01. Why I am getting two values? Is this a problem with convergence or something ?
02. If this is okay, which value is the correct one?

I have 216 points (6x6x6) in the mesh.

k ibnd E Im(self)
1 2 -4.2671 38.2096
2 2 -4.2208 38.0663
..................
28 2 -0.5387 40.4254
29 2 -0.3545 36.5669
30 2 -0.1692 31.3873
31 2 0.0169 26.4883
32 2 0.2035 27.9649
33 2 0.3903 25.3844
34 2 0.577 23.5522
35 2 0.7633 22.4693
...................
59 2 5.0381 0
60 2 5.2306 0
61 2 5.4272 0
62 2 5.6282 0
63 2 5.8338 0
64 2 6.0441 0
.................
182 2 1.2813 22.5014
183 2 1.0621 23.9574
184 2 0.8474 26.039
185 2 0.6379 27.3587
186 2 0.434 29.0741
187 2 0.2361 31.7891
188 2 0.0447 31.3564
189 2 -0.1397 35.4306
190 2 -0.3168 40.7131
191 2 -0.4859 45.0103
192 2 -0.6466 47.7818
193 2 -0.7981 49.5904
194 2 -0.9395 52.3621
195 2 -1.0695 53.2035


Thank you for your support

Inoka

[sponce]

Dear Inoka,

The Imaginary part of Sigma should be 0 at the Fermi level (or at least very small) at 0K with very small broadening.

You can also see that both your point do not have exactly the same energy "0.0169" and "0.0447".

In addition, are you sure that this is the Fermi level?

The Fermi level is NOT at "0" energy by default (it can be by luck). The Fermi level is the energy at which the occ is 0.

This is the same reasoning as in Quantum Espresso.

Best,

Samuel

[inoka]

Dear Dr. Samuel

Thank you for your reply. I believed in the linewidth.elself file, E (ibnd) is with respect to fermi energy.( If you see the previous reply of this conversation Carla also has confirmed it) For my case my fermi energy is around 7eV. But in linewith.elself energy has varied only between -6 to 5 eV and Im(electron self E) is not zero at 0 eV.

I saw for graphene in J.Noffsinger's paper(2010), Fig5b. But I am not getting that shape. Am I am using a wrong file?

Further I am going to calculate electron relaxation time 'tau' using tau=hbar/(2ImS) where ImS is imaginary part of electron self energy at Fermi energy. Thus I believe Im (sigma) cannot be zero at Fermi energy.

Could you please tell me , ImS should be zero at 0K or at any temperature? The listed data before is for 300K.

Yes, I am having two values ( exactly, I am getting two parallel curves one above the other for the above data and same for the other higher temperatures I calculated). That is why I was wondering which one to select.

My wannier and DFT bands for this calculation are in a good agreement.

Please let me know if you think my method and the values are wrong.


Thank you

Inoka

[sponce]

Dear Inoka,

You are correct. The energy in linewidth.elself is with respect to Fermi energy: E-E_F.

Yes Im(sigma) has to be 0 at the Fermi level. You can look at Fig. 5.a from http://www.sciencedirect.com/science/ar ... 5516302260.

The two dips are at the Fermi level. As you increase the broadening, this increases (Fig 5.c).
Temperature acts as a broadening mechanisms and therefore it will be non-zero (but should be small) for finite temperature.

I'm not sure to understand what you mean by "two parallel curves". Could you add electronic BS of your system?

Best,

Samuel

[inoka]

Dear Dr. Samuel

Thank you for your reply. Sorry, I didn't get what is electronic BS? do you need me to add my output file?

I plotted ImS Vs E(ibnd) graph from the data in the linewidth.elself to get ImS at Fermi level. I copied the data below for 400K. I used the same k mesh path as in diamond example L-Gamma-X with 6x6x6 mesh. Thus do I need to get the same shape as in your paper if I plot the ImS Vs ik from the data below(But I do not get )?

Electron lifetime (meV)
ik ibnd E(ibnd) Im(Sgima)(meV)
1 2 -4.26708 0.000000
2 2 -4.22084 0.000000
3 2 -4.13863 0.000000
4 2 -4.04274 0.000000
5 2 -3.94014 0.000000
6 2 -3.83304 0.000000
7 2 -3.72216 0.000000
8 2 -3.60772 0.000000
9 2 -3.48971 0.000000
10 2 -3.36805 0.000000
11 2 -3.24264 0.000000
12 2 -3.11337 0.000000
13 2 -2.98014 0.000000
14 2 -2.84289 0.000000
15 2 -2.70159 0.000000
16 2 -2.55622 0.000000
17 2 -2.40683 0.000000
18 2 -2.25347 0.000000
19 2 -2.09626 0.000000
20 2 -1.93531 0.000000
21 2 -1.77080 0.000000
22 2 -1.60292 0.000000
23 2 -1.43189 0.000000
24 2 -1.25795 42.734981
25 2 -1.08137 46.514515
26 2 -0.90244 46.110758
27 2 -0.72145 43.295342
28 2 -0.53871 40.425367
29 2 -0.35453 36.566903
30 2 -0.16923 31.387263
31 2 0.01688 26.488267
32 2 0.20347 27.964866
33 2 0.39027 25.384417
34 2 0.57697 23.552151
35 2 0.76332 22.469300
36 2 0.94907 21.252131
37 2 1.13400 18.893678
38 2 1.31792 14.542410
39 2 1.50069 0.000000
40 2 1.68218 0.000000
41 2 1.86232 0.000000
42 2 2.04108 0.000000
43 2 2.21846 0.000000
44 2 2.39453 0.000000
45 2 2.56937 0.000000
46 2 2.74314 0.000000
47 2 2.91602 0.000000
48 2 3.08826 0.000000
49 2 3.26011 0.000000
50 2 3.43190 0.000000
51 2 3.60397 0.000000
52 2 3.77669 0.000000
53 2 3.95045 0.000000
54 2 4.12566 0.000000
55 2 4.30275 0.000000
56 2 4.48213 0.000000
57 2 4.66422 0.000000
58 2 4.84941 0.000000
59 2 5.03809 0.000000
60 2 5.23058 0.000000
61 2 5.42721 0.000000
62 2 5.62821 0.000000
63 2 5.83378 0.000000
64 2 6.04407 0.000000
65 2 6.25912 0.000000
66 2 6.47894 0.000000
67 2 6.70343 0.000000
68 2 6.93243 0.000000
69 2 7.16568 0.000000
70 2 7.40286 0.000000
71 2 7.64356 0.000000
72 2 7.88728 0.000000
73 2 8.13346 0.000000
74 2 8.38147 0.000000
75 2 8.63061 0.000000
76 2 8.88013 0.000000
77 2 9.12922 0.000000
78 2 9.37703 0.000000
79 2 9.62269 0.000000
80 2 9.86527 0.000000
81 2 10.10386 0.000000
82 2 10.33752 0.000000
83 2 10.56531 0.000000
84 2 10.78630 0.000000
85 2 10.99956 0.000000
86 2 11.20422 0.000000
87 2 11.39940 0.000000
88 2 11.58428 0.000000
89 2 11.75809 0.000000
90 2 11.92012 0.000000
91 2 12.06974 0.000000
92 2 12.20641 0.000000
93 2 12.32974 0.000000
94 2 12.43954 0.000000
95 2 12.53587 0.000000
96 2 12.61913 0.000000
97 2 12.69006 0.000000
98 2 12.74970 0.000000
99 2 12.79919 0.000000
100 2 12.83965 0.000000
101 2 12.87202 0.000000
102 2 12.84052 0.000000
103 2 12.79826 0.000000
104 2 12.74561 0.000000
105 2 12.68305 0.000000
106 2 12.61108 0.000000
107 2 12.53028 0.000000
108 2 12.44128 0.000000
109 2 12.34475 0.000000
110 2 12.24139 0.000000
111 2 12.13192 0.000000
112 2 12.01709 0.000000
113 2 11.89762 0.000000
114 2 11.77427 0.000000
115 2 11.64777 0.000000
116 2 11.51881 0.000000
117 2 11.38808 0.000000
118 2 11.25622 0.000000
119 2 11.12384 0.000000
120 2 10.99148 0.000000
121 2 10.85967 0.000000
122 2 10.72886 0.000000
123 2 10.59947 0.000000
124 2 10.47184 0.000000
125 2 10.34628 0.000000
126 2 10.22303 0.000000
127 2 10.10227 0.000000
128 2 9.98409 0.000000
129 2 9.86849 0.000000
130 2 9.75527 0.000000
131 2 9.64395 0.000000
132 2 9.53350 0.000000
133 2 9.42183 0.000000
134 2 9.30590 0.000000
135 2 9.17257 0.000000
136 2 9.03547 0.000000
137 2 8.90159 0.000000
138 2 8.77019 0.000000
139 2 8.63997 0.000000
140 2 8.50969 0.000000
141 2 8.37901 0.000000
142 2 8.24822 0.000000
143 2 8.11772 0.000000
144 2 7.98784 0.000000
145 2 7.85882 0.000000
146 2 7.73086 0.000000
147 2 7.60409 0.000000
148 2 7.47862 0.000000
149 2 7.35447 0.000000
150 2 7.23160 0.000000
151 2 7.10984 0.000000
152 2 6.98892 0.000000
153 2 6.86838 0.000000
154 2 6.74762 0.000000
155 2 6.62581 0.000000
156 2 6.50194 0.000000
157 2 6.37480 0.000000
158 2 6.24310 0.000000
159 2 6.10549 0.000000
160 2 5.96076 0.000000
161 2 5.80791 0.000000
162 2 5.64627 0.000000
163 2 5.47554 0.000000
164 2 5.29574 0.000000
165 2 5.10722 0.000000
166 2 4.91049 0.000000
167 2 4.70625 0.000000
168 2 4.49526 0.000000
169 2 4.27834 0.000000
170 2 4.05631 0.000000
171 2 3.83001 0.000000
172 2 3.60028 0.000000
173 2 3.36793 0.000000
174 2 3.13375 0.000000
175 2 2.89851 0.000000
176 2 2.66296 0.000000
177 2 2.42782 0.000000
178 2 2.19377 0.000000
179 2 1.96148 0.000000
180 2 1.73158 0.000000
181 2 1.50467 0.000000
182 2 1.28132 19.966226
183 2 1.06207 23.956875
184 2 0.84745 26.039038
185 2 0.63794 27.358697
186 2 0.43402 29.074091
187 2 0.23614 31.789113
188 2 0.04475 31.356362
189 2 -0.13971 35.430629
190 2 -0.31677 40.713120
191 2 -0.48594 45.010341
192 2 -0.64663 47.781763
193 2 -0.79813 49.590441
194 2 -0.93952 52.361978
195 2 -1.06955 53.172507
196 2 -1.18649 51.560841
197 2 -1.28795 45.538732
198 2 -1.37078 0.000000
199 2 -1.43116 0.000000
200 2 -1.46523 0.000000
201 2 -1.47027 0.000000

I really appreciate your support and sorry for taking your time.

Inoka

[sponce]

Dear Inoka,

I meant "electronic bandstructure".

To get something similar to my B-doped diamond plot from the paper, you need to integrate on to a quite dense q-point grid.
You need to do a convergence study with respect to that.

Can you also plot the data to a figure to see if it look similar?

Best,

Samuel

[inoka]

Dear Dr. Samuel

In the epw calculation I used the same dense mesh as in diamond example. (k mesh is 6x6x6 and for q also 6x6x6)
Also please find my plots for data in linewidth.elself. I plotted Im.(self energy) along k-mesh as well wrt (E-Ef).

https://drive.google.com/open?id=0B47VtBcBE0Cqa2d5dV9NLTk4TW8

Please let me know why I am getting a different shape.Thank you in advance for your great support

Regards
Inoka

[sponce]

Dear Inoka,

Can you share your epw input file?

I suspect that the fsthick might not be large enough.

Best,

Samuel