Rasmussen, F., Thygesen, K. S.
Phys. Chem. C, 2015, 119 (23), pp 13169–13183, April 30, 2015
This database contains calculated structural and electronic properties of a range of 2D materials. The database contains the results presented in the following paper:
Rasmussen, F., Thygesen, K. S.
Phys. Chem. C, 2015, 119 (23), pp 13169–13183, April 30, 2015
Download raw data: c2dm.db
The structures were first relaxed using the PBE xcfunctional and a 18x18x1 kpoint sampling until all forces on the atoms where below 0.01 eV/Å. The rows with xc=’PBE’ contains data from these calculations.
For materials that were found to be semiconducting in the PBE calculations we furthermore performed calculations using the LDA and GLLBSC xc functionals and the lattice constants and atom positions found from the PBE calculation. For these calculations we used a 30x30x1 kpoint sampling. For the GLLBSC calculations we calculated the derivative discontinuity and have added this contribution to the electronic band gaps. Data for these calculations are found in rows with xc=’GLLBSC’ and xc=’LDA’, respectively.
Furthermore, we calculated the G0W0 quasiparticle energies using the wavefunctions and eigenvalues from the LDA calculations and a planewave cutoff energy of at least 150 eV. The quasiparticle energies where further extrapolated to infinite cutoff energy via the methods described in the paper. The LDA rows thus further have keyvalue pairs with the results from the G0W0 calculations.
key 
description 
unit 

a 

cbm 
Conduction band minimum relative to vacuum 
eV 
cbm_g0w0 
Conduction band minimum relative to vacuum 
eV 
dir_gap 
Direct band gap 
eV 
dir_gap_g0w0 
Direct band gap 
eV 
emass1_g0w0 
Electron mass (direction 1  smallest) 
\(m_e\) 
emass2_g0w0 
Electron mass (direction 2  largest) 
\(m_e\) 
hform 
Heat of formation 
eV 
hform_fere 
Heat of formation based on fitted elemental phase reference energies 
eV 
hmass1_g0w0 
Hole mass (direction 1  smallest) 
\(m_e\) 
hmass2_g0w0 
Hole mass (direction 2  largest) 
\(m_e\) 
ind_gap 
Indirect band gap 
eV 
ind_gap_g0w0 
Indirect band gap 
eV 
name 

phase 
Phase 

project 

q2d_macro_df_slope 
Slope of macroscopic 2D static dielectric function at q=0 
? 
vbm 
Valence band maximum relative to vacuum 
eV 
vbm_g0w0 
Valence band maximum relative to vacuum 
eV 
xc 
Exchangecorrelation (XC) energy functional 
The following python script shows how to plot the positions of the VBM and CBM.
# creates: bandalignment.png
from math import floor, ceil
import re
import numpy as np
import matplotlib.pyplot as plt
import ase.db
# Connect to database
db = ase.db.connect('c2dm.db')
# Select the rows that have G0W0 results
rows = db.select('xc=LDA,ind_gap_g0w0>0')
data = []
for row in rows:
name = row.name
# Use regular expressions to get the atomic species from the name
m = re.search('([AZ][az]?)([AZ][az]?)2', name)
M = m.group(1)
X = m.group(2)
label = ''
if row.phase == 'H':
label += '2H'
elif row.phase == 'T':
label += '1T'
label += name.replace('2', '$_2$')
# Store data as tuples  easier to sort
data.append((M, X, label, row.vbm_g0w0, row.cbm_g0w0))
# Sort according to atomic species (alphabetically)
data.sort(key=lambda tup: (tup[1], tup[0]))
label_list = [tup[2] for tup in data]
vbm_list = [tup[3] for tup in data]
cbm_list = [tup[4] for tup in data]
x = np.arange(len(vbm_list))
emin = floor(min(vbm_list))  1.0
emax = ceil(max(cbm_list)) + 1.0
# With and height in pixels
ppi = 100
figw = 800
figh = 400
fig = plt.figure(figsize=(figw / ppi, figh / ppi), dpi=ppi)
ax = fig.add_subplot(1, 1, 1)
ax.bar(x + 0.1, np.array(vbm_list)  emin, bottom=emin, color='#A3C2FF')
ax.bar(x + 0.1, emax  np.array(cbm_list), bottom=cbm_list, color='#A3C2FF')
ax.set_xlim(0, len(vbm_list))
ax.set_ylim(emin, emax)
ax.set_xticks(x + 0.5)
ax.set_xticklabels(label_list, rotation=90, fontsize=10)
ax.tick_params(axis='y', labelsize=10)
plt.title('Positions of VBM and CBM', fontsize=12)
plt.ylabel('Energy relative to vacuum (eV)', fontsize=10)
plt.tight_layout()
plt.savefig('bandalignment.png')
This produces the figure