CI¶

Keywords for the CI input block. These keywords control the behaviour of the CI-solvers used in HUMMR.

Keyword	Format	Description	Default
`BatchHCINEVPT2`	`bool`	Flag for doing doing the batching in a HCI-NEVPT2 calculation. With `false`, the memory usage will be significantly larger but the calculation will be faster.	`true`
`DavidsonGuessDim`	`integer`	Dimension of the subspace Hamiltonian from which the initial guess-vector for the Davidson procedure is obtained.	`1024`
`DavidsonMaxIter`	`integer`	Maximum number of iterations for the Davidson diagonalization.	`50`
`DavidsonMaxSize`	`integer`	Maximum number of expansion vectors in the Davidson procedure before the iterative subspace is collapsed.	`500`
`DavidsonPCDim0`	`integer`	Dimension of the 0^th subspace in the Davidson preconditioner based on https://doi.org/10.1002/jcc.1111. Modify only in special cases, e.g. strong electron correlation. If not chosen by the user, the program determines its value automatically based on a heuristic.	`512`
`DavidsonPCDim1`	`integer`	Dimension of the 1^st subspace in the Davidson preconditioner based on https://doi.org/10.1002/jcc.1111. Modify only in (very) special cases, e.g. strong electron correlation. If not chosen by the user, the program determines its value automatically based on a heuristic.	`0`
`DavidsonRTol`	`double`	Threshold (residual norm) for controlling the convergence of the Davidson diagonalization.	`1e-6`
`DoCIPSIOnHCI`	`bool`	Use CIPSI-pruning in the configuration selection procedure.	`true`
`DoHCIPT2`	`bool`	Calculate the second-order perturbative correction in the HCI calculation. Note that the PT2-correction is calculated only in the end of the CASSCF-calculation.	`true`
`EpsilonGen`	`double`	Threshold for choosing the generator configurations in a selective-CI (HCI) calculation.	`1e-2`
`EpsilonHCI`	`double`	Threshold for selecting configurations in a HCI calculation.	`1e-5`
`EpsilonHCIPT2`	`double`	Threshold for selecting configurations during calculating the PT2-correction in HCI.	`1e-6`
`EpsilonHCINEVPT2`	`double`	Threshold for screening the 5-body residual terms in the HCI-NEVPT2 method.	`1e-7`
`EpsilonHCIENEVPT2`	`double`	Threshold for the HCI screening in the EN-HCINEVPT2 method that uses the Epstein-Nesbet Hamiltonian for the Va/Vi classes..	`1e-7`
`HCICFGsFName`	`string`	Name of the file containing starting configurations in HCI.	``
`HCIETol`	`double`	Energy threshold for signaling convergence of the HCI configuration selection iterations.	`1e-5`
`HCIMaxIter`	`integer`	Maximum number of iterations in the HCI calculation.	`20`
`MaxPrefixBatchSize`	`integer`	Maximum number of prefixes in a batch in the HCI prefix method. Larger value increases the peak memory usage.	`1000`