```
subroutine obtain_h2_psi()
real(dp) :: dummy_sign(lenof_sign)
! apply H once, we now have the spawnedParts from a single iteration
call apply_hamiltonian(CurrentDets, int(TotWalkers), .true., tTruncInitiator, .true.)
! communicate the spawns between processors and store the compressed spawns into a buffer
call generate_spawn_buf()
! apply H to the buffer to get H^2 on the original population. The result is stored
! in spawnedParts (uncommunicated)
call apply_hamiltonian(spawnBuf, spawnBufSize, .false., .false., .false.)
! communicate the result and compress the population (such that each determinant
! only occurs once)
call SendProcNewParts(spawnBufSize, .false.)
call CompressSpawnedList(spawnBufSize, iter_data_fciqmc)
end subroutine obtain_h2_psi
```

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