# Double-hybrid calculation: isomers propyne and propadiene¶

This tutorial will show you how to do calculate the energy difference between the structural isomers propyne and propadiene.

In this example double-hybrids are used. Note that this example is an example in which double-hybrids typically improve over standard GGA or hybrid functionals.

An all electron TZ2P basis set is used since that is the recommended choice in ADF for double hybrids. For reasons of numerical stability, it is also highly recommended not to use larger or more diffuse basis sets. The use of triple-zeta quality basis sets is usually necessary for accurate double-hybrid energies. In ADF one can only do single point calculations in case of double-hybrids.

## Step 1: Propyne¶

Start a new ADFinput
Copy-paste the following coordinates of propyne:
C          0.00000000      0.00000000     -0.95122586
C          0.00000000      0.00000000      0.50451101
C          0.00000000      0.00000000      1.70543908
H         -0.51019468     -0.88368312     -1.34212552
H         -0.51019468      0.88368312     -1.34212552
H          1.02038937      0.00000000     -1.34212552
H          0.00000000      0.00000000      2.76765234

XC functional: Double Hybrids → rev-DOD-PBEP86-D4.
Basis set: TZ2P.
Frozen core: None.
Click on File → Save As… and give it the name “Propyne”.
Click on File → Run.
Wait for the calculation to finish.

## Step 2: Propadiene¶

Delete all atoms
Copy-paste the following coordinates of propadiene:
C          0.00000000      0.00000000      0.00000000
C          0.00000000      0.00000000     -1.30115735
C          0.00000000      0.00000000      1.30115735
H         -0.65550932     -0.65550932     -1.86483287
H          0.65550932      0.65550932     -1.86483287
H         -0.65550932      0.65550932      1.86483287
H          0.65550932     -0.65550932      1.86483287

Click on File → Save As… and give it the name “Propadiene”.
Click on File → Run.
Wait for the calculation to finish.

## Step 3: Energy difference¶

If one compares the bond energy printed in Propyne.logfile with that of Propadiene.logfile, one finds that with the used double hybrid rev-DOD-PBEP86-D4 propyne is around 1.9 kcal/mol lower in energy than propadiene.