Tip

All input files can be downloaded: Files.

xtb

This keyword controls the xTB calculation options.

Options

chrg

Value

An integer

Default

0

The total charge of the system.

uhf

Value

An integer

Default

0

The number of unpaired electrons.

gfn

Value

1 The GFN1-xTB Hamiltonian.

2 The GFN2-xTB Hamiltonian.

Default

2

Define the xTB Hamiltonian type.

gbsa

Value

H2O

Acetone

Acetonitrile

Benzene

CH2Cl2

CHCl3

CS2

DMSO

Ether

Hexane

Toluene

THF

Default

None

The solvent name. If it is not given, the xTB is calculated in the gas phase. Otherwise, generalized Born model will be used to consider solvent effects.

etemp

Value

A real number

Default

300

The electronic temperature in Kelvin.

vparam

Value

A file name for the xTB parameter file.

Default

None

If not given, the default parameters stored internally in Qbics will be used. If a file name (path can be included) is given, the xTB calculation will use the parameters in this file.

Theoretical Background

xTB is a powerful semiempirical quantum chemical method proposed by Stefan Grimme. It has been designed for the purpose of facilitating rapid and accurate electronic structure calculations of large molecular systems (approximately 1000 atoms). It can be used to rapidly give good initial guess for DFT calculations.

xTB has several Hamiltonians. Qbics supports GFN-1 and GFN-2. It seems that:

  • GFN1-xTB: When a system contains metal cluster-like structures, this is better.

  • GFN2-xTB: For most organic molecules with no or a few metal atoms.

To consider solvent effects, one can use gbsa.

xTB can also work with CHARMM force field, i.e., xTB/MM method. This is a powerful way to study large, complicated systems.

For all features of xTB method, please refer to the xTB manual.

Input Examples

In all examples below, you can change opt to md to do molecular dynamics.

Example: Geometry Optimization by GFN2-xTB for Cantharidin

Perform geometry optimization by GFN2-xTb for an organic molecule cantharidin:

xtb-1.inp
 1xtb
 2    chrg 0
 3    gfn  2  # GFN2-xTB.
 4end
 5
 6# Cantharidin
 7mol
 8    C    1.39900    0.71500    1.06800
 9    C    1.92100    -0.06900    -0.14800
10    C    0.78600    -0.69800    -1.04400
11    C    0.13800    -2.16200    -0.87800
12    C    1.29700    -3.05700    -0.50500
13    C    2.44700    -2.21000    -1.00400
14    O    1.70700    -1.35300    -1.91200
15    C    2.98300    -1.16300    -0.03500
16    C    3.42500    -1.73000    1.31300
17    C    4.18700    -0.54700    -0.69400
18    O    5.29000    -1.08800    -0.78200
19    O    3.91700    0.65900    -1.20900
20    C    2.61300    0.98300    -0.99400
21    O    2.10200    2.01700    -1.40000
22    H    0.94400    0.07300    1.82400
23    H    0.61300    1.41400    0.73300
24    H    2.16400    1.34500    1.53700
25    H    0.05600    -0.55500    -0.22800
26    H    -0.28600    -2.46400    -1.85300
27    H    -0.70400    -2.25200    -0.17500
28    H    1.22700    -4.00600    -1.04600
29    H    1.31500    -3.28300    0.56100
30    H    3.20900    -2.78100    -1.54000
31    H    2.64400    -2.28900    1.83300
32    H    3.79300    -0.95400    1.99200
33    H    4.26100    -2.43200    1.16600
34end
35
36task
37    opt xtb
38end

Example: Geometry Optimization by GFN1-xTB for Co6Te8(P(Et)3)6

Perform geometry optimization by GFN1-xTB for a quantum dot Co6Te8(P(Et)3)6. For such inorganic systems, GFN2-xTB may not converge.

xtb-2.inp
  1xtb
  2    chrg 0
  3    gfn  1  # GFN1-xTB. Do you want to try GFN2-xTB?
  4end
  5
  6# Quantum dot: Co6Te8(P(Et)3)6
  7mol
  8    Co    0.07482    0.19972    2.25274
  9    Co    -0.57236    2.10842    -0.12184
 10    Co    2.14275    0.01139    -0.00690
 11    Co    0.05260    -2.18506    -0.00075
 12    Co    -0.03312    0.01926    -2.21965
 13    Co    -2.27062    -0.26857    0.13243
 14    Te    -1.92498    1.48104    1.75344
 15    Te    1.51638    1.80079    -1.53651
 16    Te    -1.62601    -1.71313    -1.72073
 17    Te    -1.37710    -1.68992    1.91428
 18    Te    1.61324    -1.60191    1.77284
 19    Te    -2.00357    1.32469    -1.66240
 20    Te    1.66650    -1.63285    -1.74916
 21    Te    1.57938    1.94121    1.38532
 22    P    -4.02850    -1.49064    0.26273
 23    C    -5.19829    -1.41084    -1.21441
 24    H    -4.71377    -1.92702    -2.04886
 25    H    -6.13262    -1.93467    -0.99467
 26    C    -5.52751    0.01728    -1.64482
 27    H    -6.14156    0.00324    -2.54679
 28    H    -6.07317    0.54663    -0.86250
 29    H    -4.61066    0.57223    -1.85793
 30    C    -5.30003    -1.10968    1.60881
 31    H    -5.85560    -0.21489    1.31212
 32    H    -6.02467    -1.92631    1.68168
 33    C    -4.67909    -0.85880    2.97985
 34    H    -5.45790    -0.66760    3.72007
 35    H    -4.08936    -1.71732    3.30379
 36    H    -4.01919    0.01101    2.93660
 37    C    -3.88381    -3.34584    0.48895
 38    H    -3.69815    -3.52421    1.55200
 39    H    -2.98357    -3.67170    -0.04002
 40    C    -5.05361    -4.21895    0.03691
 41    H    -4.86097    -5.25352    0.32700
 42    H    -5.98965    -3.90442    0.49944
 43    H    -5.17056    -4.18666    -1.04614
 44    P    4.26310    -0.30746    0.15884
 45    C    5.20849    0.27270    -1.36436
 46    H    4.75167    1.21294    -1.69163
 47    H    6.25460    0.48490    -1.12936
 48    C    5.15727    -0.72993    -2.51672
 49    H    5.46512    -0.25078    -3.44736
 50    H    5.81933    -1.57520    -2.32685
 51    H    4.14177    -1.11524    -2.64233
 52    C    5.11814    -1.95972    0.40905
 53    H    4.65430    -2.67193    -0.28084
 54    H    6.17155    -1.88201    0.12313
 55    C    5.02841    -2.52709    1.82421
 56    H    5.41753    -3.54657    1.84052
 57    H    5.60186    -1.92517    2.52917
 58    H    3.98817    -2.54672    2.15600
 59    C    5.07249    0.73925    1.49299
 60    H    4.67423    0.39189    2.45186
 61    H    4.69613    1.75999    1.36590
 62    C    6.59882    0.77674    1.57721
 63    H    6.89665    1.35016    2.45694
 64    H    7.01872    -0.22476    1.66541
 65    H    7.03038    1.25623    0.69893
 66    P    0.54020    0.66347    -4.18625
 67    C    0.22564    2.40032    -4.82496
 68    H    0.71085    3.09306    -4.13064
 69    H    0.69956    2.53727    -5.80137
 70    C    -1.25205    2.77005    -4.94545
 71    H    -1.35213    3.83547    -5.15929
 72    H    -1.73005    2.21033    -5.75002
 73    H    -1.77854    2.55103    -4.01396
 74    C    -0.31031    -0.32739    -5.55031
 75    H    -1.38586    -0.13635    -5.48194
 76    H    0.01101    0.00196    -6.54210
 77    C    -0.07813    -1.83035    -5.40257
 78    H    -0.63237    -2.37433    -6.16909
 79    H    0.97995    -2.07651    -5.49904
 80    H    -0.42183    -2.16791    -4.42187
 81    C    2.34305    0.47110    -4.66339
 82    H    2.65871    -0.51529    -4.31013
 83    H    2.90238    1.20335    -4.07212
 84    C    2.73771    0.61134    -6.13325
 85    H    3.82165    0.51779    -6.22187
 86    H    2.28001    -0.16835    -6.74157
 87    H    2.44775    1.58156    -6.53622
 88    P    0.62497    1.10725    4.12138
 89    C    2.39189    1.12488    4.75495
 90    H    2.99045    1.67998    4.02630
 91    H    2.45236    1.66544    5.70425
 92    C    2.99908    -0.26481    4.94187
 93    H    4.06777    -0.18045    5.14607
 94    H    2.52854    -0.78692    5.77566
 95    H    2.86297    -0.86705    4.04081
 96    C    -0.20941    0.28666    5.60490
 97    H    0.15369    -0.74420    5.66370
 98    H    0.07196    0.77828    6.54013
 99    C    -1.73060    0.25398    5.47187
100    H    -2.17355    -0.26257    6.32492
101    H    -2.14306    1.26238    5.42400
102    H    -2.01420    -0.27566    4.55989
103    C    0.18744    2.91028    4.39005
104    H    -0.80673    3.06756    3.95946
105    H    0.88329    3.49228    3.77726
106    C    0.19716    3.46228    5.81507
107    H    0.01322    4.53785    5.78327
108    H    -0.58383    3.00325    6.42068
109    H    1.15764    3.29671    6.30321
110    P    0.50037    -4.23165    -0.45649
111    C    0.33638    -4.95275    -2.18024
112    H    0.88223    -4.28949    -2.85878
113    H    0.82383    -5.93134    -2.22239
114    C    -1.09935    -5.10086    -2.67831
115    H    -1.09940    -5.40811    -3.72540
116    H    -1.64199    -5.84739    -2.09777
117    H    -1.62712    -4.14741    -2.59715
118    C    -0.42694    -5.55682    0.51882
119    H    -1.48401    -5.50017    0.24082
120    H    -0.08115    -6.55916    0.25173
121    C    -0.31641    -5.35550    2.02886
122    H    -0.92092    -6.09745    2.55307
123    H    0.71702    -5.44947    2.36437
124    H    -0.67723    -4.36005    2.30237
125    C    2.28540    -4.69974    -0.10975
126    H    2.56512    -4.22430    0.83575
127    H    2.88463    -4.21217    -0.88607
128    C    2.66107    -6.17949    -0.04535
129    H    3.74212    -6.26881    0.07682
130    H    2.18351    -6.67142    0.80162
131    H    2.37807    -6.70546    -0.95721
132    P    -1.88362    3.80220    0.05043
133    C    -3.72133    3.80113    0.43439
134    H    -3.92611    2.89184    1.00638
135    H    -3.95713    4.64298    1.09168
136    C    -4.66286    3.84410    -0.76765
137    H    -5.68683    3.66404    -0.43496
138    H    -4.62838    4.81311    -1.26529
139    H    -4.39293    3.06880    -1.48575
140    C    -1.85215    4.95783    -1.44558
141    H    -2.32560    4.43432    -2.28107
142    H    -2.43731    5.86170    -1.25698
143    C    -0.43388    5.34449    -1.86016
144    H    -0.45831    5.92448    -2.78423
145    H    0.05377    5.94199    -1.08916
146    H    0.16816    4.44750    -2.03047
147    C    -1.28938    4.97422    1.41176
148    H    -0.19434    4.95693    1.40891
149    H    -1.60040    4.51594    2.35618
150    C    -1.76235    6.42709    1.38328
151    H    -1.44247    6.92890    2.29841
152    H    -1.33556    6.96411    0.53662
153    H    -2.84893    6.49209    1.32206
154end
155
156task
157    opt xtb
158end

Example: Geometry Optimization by GFN2-xTB for Avibactam in Implicit Solvent

Perform geometry optimization by GFN2-xTB for an organic anion in implicit DMSO solvent:

xtb-3.inp
 1xtb
 2    chrg -1 # The charge is set here.
 3    gfn   2
 4    gbsa  DMSO # This is in the list of xtb/gbsa item.
 5end
 6
 7# Avibactam anion.
 8mol
 9    N    1.83500    1.56700    0.16500
10    C    2.12100    0.23900    0.16900
11    O    1.81100    -0.44100    -0.81200
12    C    2.91300    -0.26000    1.37900
13    C    3.39800    -1.72600    1.24400
14    C    3.05700    -2.71300    2.38100
15    C    2.33800    -2.11500    3.59200
16    C    1.27000    -1.15400    3.10000
17    C    2.15100    0.03200    2.68300
18    C    3.19600    0.07600    3.78800
19    O    3.93800    1.02100    3.98300
20    N    3.17400    -1.18300    4.31100
21    O    4.05400    -1.65700    5.28400
22    S    3.38300    -1.70500    6.79900
23    O    4.42700    -2.31500    7.61600
24    O    3.08700    -0.30900    7.10900
25    O    2.19100    -2.53900    6.62800
26    H    1.26500    1.98900    -0.55600
27    H    2.09600    2.17600    0.93800
28    H    3.82300    0.36100    1.36100
29    H    4.49300    -1.70100    1.15700
30    H    3.06500    -2.17300    0.29900
31    H    3.97500    -3.21900    2.70500
32    H    2.41300    -3.49600    1.96000
33    H    1.94500    -2.89800    4.24100
34    H    0.61200    -0.86000    3.92800
35    H    0.65100    -1.55100    2.29000
36    H    1.57300    0.96000    2.68200
37end
38
39task
40    opt xtb
41end

Example: Geometry Optimization by for Organic Radical C13H9

Perform geometry optimization by GFN2-xTB for an organic radical C13H9:

xtb-4.inp
 1xtb
 2    chrg  0
 3    gfn   2
 4    uhf   1 # The number of unpaired electrons is 1.
 5end
 6
 7# C13H9
 8mol
 9    C  0.   -1.2266   -2.135
10    C  0.    0.0000   -1.424
11    C  0.    1.2266   -2.135
12    C  0.   -2.4574   -1.388
13    C  0.    0.0000    0.008
14    C  0.   -1.2295    0.717
15    C  0.   -2.4588   -0.032
16    C  0.   -1.2128    2.117
17    H  0.   -2.1632    2.672
18    C  0.    0.0000    2.807
19    C  0.    1.2128    2.117
20    C  0.    1.2295    0.717
21    C  0.    2.4588   -0.032
22    C  0.    2.4574   -1.388
23    H  0.    3.4035   -1.951
24    H  0.    3.4010    0.542
25    H  0.   -3.4035   -1.951
26    H  0.   -3.4010    0.542
27    H  0.    0.0000    3.908
28    H  0.    2.1632    2.672
29    H  0.   -1.2130   -3.109
30    H  0.    1.2130   -3.109
31end
32
33task
34    opt xtb
35end