Dear Pennylane team,

I’ve buid a number of molecular Hamiltonians and quantum circuits by using the calls

`qchem.molecular_hamiltonian()`

and `ApproxTimeEvolution()`

.

Most molecules I’ve tried are toy examples and featured in the Pennylane tutorials or documentation pages. I’ve tried: LiH, H2O and H2.

For these small molecules Pennylane computes Hamiltonians and respective quantum circuits in few minutes.

However, recently I’ve tried to get a Hamiltonian and a quantum circuit for

the C2HF3 molecule. The geometry is as follows:

```
symbols = ["C", "C", "F", "F", "F", "H"]
coordinates = np.array(
[
0.0, 0.430631, 0.000000,
-0.704353, -0.686847, 0.0,
1.314791, 0.500587, 0.0,
-0.554822, 1.630861, 0.0,
-0.092517, -1.882156, 0.0,
-1.780948, -0.706341, 0.0
]
)
hamiltonian, num_qubits = qchem.molecular_hamiltonian(symbols, coordinates)
print(f"Number of qubits: {num_qubits}")
print("Qubit Hamiltonian")
print(hamiltonian)
```

This is a larger molecule and Pennylane is not able to compute a Hamiltonian let alone the circuit. That is, calling `qchem.molecular_hamiltonian()`

runs for hours and never terminates.

Any ideas on how to get a Hamiltonian and a circuit in reasonable time (say few minutes)? What do I miss here?

P.S. I tried the same molecule in a different quantum chem python package and it was able to produce a Hamiltonian and a respective circuit in under 2 minutes.