From Diracwiki

Spin-free relativistic GASCI module written by Jeppe Olsen, adaptation to DIRAC by Timo Fleig, parallelization by Stefan Knecht

LUCITA is a string-based Hamiltonian-direct configuration interaction (CI) program, based on the LUCIA code ^[1]. It is capable of doing efficient CI computations at arbitrary excitation level, e.g. FCI, SDCI, RASCI, and MRCI using general active spaces. The code is interfaced ^[2] to molecular integrals obtained in the spin-free Dirac formalism and uses non-relativistic point group symmetry. It is implemented as a full parallel version ^[3].

A central feature of the program is the Generalized Active Space (GAS) concept, in which the underlying total orbital space is subdivided into a basically arbitrary number (save for an upper limit) of subspaces with arbitrary occupation constraints. This is the most general approach to orbital space subdivisions. The program uses DIRAC orbitals from either a closed- or an open-shell calculation in a spin-free relativistic formalism or the non-relativistic Lévy-Leblond formalism (see **HAMILTONIAN).

The technical limitations are roughly set by several 100 million determinants in the CI expansion on PCs and common computing clusters and several billions of determinants on supercomputers with ample memory. For calculations involving more than 500.000 determinants and in particular higher than double excitations it is strongly recommended to use LUCITA in spin-free DIRAC applications.

If desired, the program also computes 1- and 2-particle densities from optimized CI wave functions. The density matrices may be printed along with natural orbital occupations and the corresponding eigenvectors (NOs).

LUCITA is provided with an interface section DIRLUC incorporated in the code. The DIRLUC environment reads the DIRAC input and converts it to a LUCIA input which is processed through an ASCII file (LUCIAIN). The types of CI which may be specified by keyword are: Full CI (FCI), CI with single and double excitations (SDCI), CI with single, double, triple, and quadruple excitations (SDTQ), restricted active space CI (RASCI), and generalized active space CI (GASCI). All types of CI can be considered special cases of a GASCI, so internally, DIRLUC transfers all information into GAS format. More detailed information on GAS-type of wavefunctions can be found in the literature ^[4].

Contents 1 Important Information for Users 2 Mandatory keywords 2.1 .INIWFC 2.2 .CITYPE 2.3 .MULTIP 3 Optional keywords 3.1 .TITLE 3.2 .NROOTS 3.3 .SYMMET 3.4 .SZCALC 3.5 .MAXITR 3.6 .INACTI 3.7 .DENSI 3.8 .RSTRCI 3.9 .LBLKSZ 3.10 .TRUNCF 3.11 .PRINTL 3.12 .PRINTG 4 Specific input -- GASCI 4.1 .NACTEL 4.2 .GASSHE 4.3 .GASSPC 5 Specific input -- RASCI 5.1 .NACTEL 5.2 .INACTI 5.3 .RAS1 5.4 .RAS2 5.5 .RAS3 6 Parallel keywords 6.1 .DISTRT 7 References

Important Information for Users

In DIRAC08 the default integral transformation scheme has changed. Please add the lines

.SCHEME
 4

to your MOLTRA input section for the integral transformation.

Mandatory keywords

.INIWFC

Initial HF wave function, closed-shell:

.INIWFC
 DHFSCF

or open-shell:

.INIWFC
 OSHSCF

Default: None.

.CITYPE

Type of CI calculation. Typical multi-reference CI calculations should be defined by RASCI or GASCI.

Values: FCI, SDCI, SDTQ, RASCI, GASCI

Default: None.

.MULTIP

State spin multiplicity.

Default: None.

Optional keywords

.TITLE

One line with title of CI calculation.

.NROOTS

Number of states to optimize on.

Default:

.NROOTS
 1

.SYMMET

State symmetry. This is the boson symmetry label referring to an irrep ordering as defined by the group generators.

Default:

.SYMMET
 1

.SZCALC

Approximate size of calculation.

Normal CI (default):

.SZCALC
 NOR

Large CI:

.SZCALC
 LAR

Huge CI:

.SZCALC
 HUG

.MAXITR

Number of CI iterations.

Default:

.MAXITR
 100

.INACTI

Inactive orbitals per boson symmetry, separated by commas.

Not allowed with type GASCI.

Default: All orbitals active.

.DENSI

Level of computed density matrices.

For one-particle density only:

.DENSI
 1

For one- and two-particle density matrices:

.DENSI
 2

Default: calculate and print natural orbital occupation numbers.

.RSTRCI

Optional restart from CI vector on file LUCVECT resp. LUCVECT.0 (parallel calculation):

.RSTRCI
 1

Default: No restart.

.LBLKSZ

Largest allowed vector batchsize; will be determined dynamically otherwise.

Default:

.LBLKSZ
 100 000

.TRUNCF

Truncate residual vectors before creating new trial vector (use with care! experts only).

Default:

.TRUNCF
 1.0D-10

.PRINTL

Local print level for DIRLUC interface.

Default:

.PRINTL
 0

Range: 0-10

.PRINTG

Global print level for LUCIA. Use with care! Set to 1 for printing density matrices (if specified) and natural orbitals.

Default:

.PRINTG
 0

Range: 0-4

Specific input -- GASCI

.NACTEL

Number of active electrons.

Default: None.

.GASSHE

Number and specification of GAS orbitals. Line with the number of GA spaces used (1-16), followed by one line per GAS with number of orbitals per boson symmetry, separated by commas.

Default: None.

.GASSPC

Number and specification of sequential CI calculations. Line with the number of CI calculations with given GA spaces (currently only 1 is allowed), followed by one line per GAS with 2 numbers each: The first gives the minimal number of accumulated electrons after this GAS, the second the corresponding maximum number, separated by blanks (defining occupation constraints of each GAS).

Default: None.

Specific input -- RASCI

.NACTEL

Number of active electrons.

Default: None.

.INACTI

Inactive orbitals per boson symmetry, separated by commas.

Default: All orbitals active.

.RAS1

RAS1 specification and maximum number of holes. Line with orbitals per boson symmetry, separated by commas, followed by a line with the maximum number of holes in RAS1.

Default: None.

.RAS2

RAS2 specification. Line with orbitals per boson symmetry, separated by commas.

Default: None.

.RAS3

RAS3 specification and maximum number of electrons. Line with orbitals per boson symmetry, separated by commas, followed by a line with the maximum number of electrons in RAS3.

Default: None.

Parallel keywords

.DISTRT

Specifies vector block distribution routine to use in parallel calculation.

simple distribution routine useful in small calculations:

.DISTRT
 1

more advanced and efficient distribution routine:

.DISTRT
 2

Default: 2

References

1. ↑ J. Olsen and P. Joergensen and J. Simons, Passing the one-billion limit in Full CI calculations, Chem. Phys. Lett. 169, 463 (1990) .
2. ↑ T. Fleig and L. Visscher, Large-Scale Electron Correlation Calculations in the Framework of the Spin-Free Dirac Formalism. The Au₂ Molecule Revisited, Chem. Phys. 311, 113 (2005) electronic version.
3. ↑ S. Knecht and H. J. Aa. Jensen and T. Fleig, Large-Scale Parallel Configuration Interaction. I. Non-Relativistic and Scalar-Relativistic General Active Space Implementation with Application to (Rb-Ba)⁺., J. Chem. Phys. 128, 014108 (2008) electronic version.
4. ↑ T. Fleig and J. Olsen and L. Visscher, The generalized active space concept for the relativistic treatment of electron correlation: II. Large-scale configuration interaction implementation based on relativistic 2-and 4-spinors and its application., J. Chem. Phys. 119, 2963 (2003) electronic version.