# Stuck in code book exercise H.5.3

**URL:** <https://discuss.pennylane.ai/t/stuck-in-code-book-exercise-h-5-3/4350>\
**Category:** Codebook\
**Created:** [March 26, 2024, 3:54pm UTC](https://discuss.pennylane.ai/t/stuck-in-code-book-exercise-h-5-3/4350 "2024-03-26T15:54:07Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![SUDHIR\_KUMAR\_SAHOO](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sudhir_kumar_sahoo/32/2254_2.png) [@SUDHIR\_KUMAR\_SAHOO](https://discuss.pennylane.ai/u/SUDHIR_KUMAR_SAHOO)\
**Post date:** [March 26, 2024, 3:54pm UTC](https://discuss.pennylane.ai/t/stuck-in-code-book-exercise-h-5-3/4350/1 "2024-03-26T15:54:07Z")

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I have tried to solve this way. I do not know where it went wrong

```auto
def ham_close_spins(B, J):
    """Creates the Hamiltonian for two close spins.

    Args:
        B (float): The strength of the field, assumed to point in the z direction.
        J (list[float]): A vector of couplings [J_X, J_Y, J_Z].

    Returns:
        qml.Hamiltonian: The Hamiltonian of the system.
    """
    e = 1.6e-19
    m_e = 9.1e-31
    alpha = B*e/(2*m_e)
    hbar = 1e-34
    ##################
    # YOUR CODE HERE #
    ##################
    coeffs = [-alpha*hbar,-alpha*hbar, hbar*hbar*J[0]/4, hbar*hbar*J[1]/4,hbar*hbar*J[2]/4] # MODIFY THIS
    obs = [qml.PauliZ(0), qml.PauliZ(1), qml.PauliX(0)@qml.PauliX(1), qml.PauliY(0)@qml.PauliY(1), qml.PauliZ(0)@qml.PauliZ(1)] # MODIFY THIS
    return qml.Hamiltonian(coeffs, obs)

```

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<div class="post-metadata">

**Author:** ![Alvaro\_Ballon](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/alvaro_ballon/32/874_2.png) [@Alvaro\_Ballon](https://discuss.pennylane.ai/u/Alvaro_Ballon)\
**Post date:** [March 28, 2024, 1:28pm UTC](https://discuss.pennylane.ai/t/stuck-in-code-book-exercise-h-5-3/4350/2 "2024-03-28T13:28:32Z")

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Hello @SUDHIR_KUMAR_SAHOO

I think you need to multiply `alpha` in your `coeffs` by `hbar`.

Hope this helps!

Alvaro

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<div class="post-metadata">

**Author:** ![SUDHIR\_KUMAR\_SAHOO](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/sudhir_kumar_sahoo/32/2254_2.png) [@SUDHIR\_KUMAR\_SAHOO](https://discuss.pennylane.ai/u/SUDHIR_KUMAR_SAHOO)\
**Post date:** [March 28, 2024, 1:41pm UTC](https://discuss.pennylane.ai/t/stuck-in-code-book-exercise-h-5-3/4350/3 "2024-03-28T13:41:41Z")

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I got it. Thanks @Alvaro_Ballon