# Frequently Asked QuestionsΒΆ

I cannot login / I have lost the password

You can use

`reset-password`

command described in reset-pasword: Reset password to send an email for resetting the login password to your registered email address. Please reset the password by following instructions in the email.Can I know the required qubit number before computation?

Basically, the requried qubit number is equal to the twice number of molecular orbitals to be calculated. (If mapping is

*SYMMETRY_CONSERVING_BRAVYI_KITAEV*, the number of qubits is further reduced by 2 qubits.) If cas option is set, active_orb is the number of molecular orbitals to be calculated, while if cas is not set, all molecular orbitals will be calculated. In that case, for reference, in the minimum basis set, 1 orbital per H atom (1s) and 5 orbitals per O atom (1s, 2s, 2p) are required, so a water molecule H2O has 7 molecular orbitals, and the required qubit will be 14 qubits because of spin. Therefore, except for a few small molecules (H2, HeH, etc.) that are treated with small basis sets, it is better to set cas to reduce computational cost.What is the meaning of each number in overlap_weights list in VQD calculation?

For example, if overlap_weights is [4.0, 1.0], when calculating the first excited state, the weight for the first excited state and the ground state is 1.0. When calculating the second excited state, the weight for the second and first excited states is 4.0, and the weight for the second and ground states is 1.0.

Why the energies of ground state and excited state are same when I calculate triplet state?

Since the triplet state are degenerate in Sz numbers which are -1, 0, 1, you have to set Sz number and the cost function to avoid degenerate.

Why only the result of electronic ground state is outputed when I set FCI as post-HF method?

In Qamuy, we use PySCF program to do qamuy chemistry computation. Since only electronic ground state is calculated using FCI method in PySCF, Qamuy only outputs the result of electronic ground state. In stead of FCI, you can use CASCI method in Qamuy to obtain excited state.