*However, when the excitmat is returned, all elements refer to ORBITALS, NOT INDICES.**
IC should be 1 or 2, depending on whether it is a double or single excitation
Single excitations should just have ExcitMat(1,1) and ExcitMat(2,1) with orbital
information.
The algorithm could be improved for double excitations by only searching through the
determinant once, reducing it from an O[2N] to O[N] operation, though would be a little
more fiddly…
[W.D. 11.12.2017]:
never thought to touch this part of the code ever.. but we need triple excitations
now too.. so adapt this functionality here.., since this function is
unfortunately called in too many parts of the code..

#include "macros.h" !This is an O[2*N] operation for doubles or O[N] operation for single excitations. !It takes a determinant nI, and a 2x2 matrix indicating the excited 'to' and 'from' !orbitals, and finds the determinant nJ, while keeping the final determinant ordered. !This will save having to order the final determinant. !We also calculate the parity of the excitation. This is needed for the scrules as !i.e. <1 2 3 4 | H | 1 3 5 6> is - <2 4 || 5 6> but <1 2 3 4 | H | 1 2 5 6 > = +<3 4 || 5 6> !1 2 3 4 -> 1 2 5 6 , it would give 3->5 and 4->6 with a +ve parity !because no interchanges were required to line up the dets !1 2 3 4 -> 1 3 5 6 we would swap 2 and 3 around to give a negative parity and have 2->5 and 4->6 !so I just need to work out how much the common orbitals between the determinants have moved between !the ordered list of orbitals. If its an even number, parity is positive (false), otherwise negative (true). !ExcitMat(1,*) are the **indices** in the determinant to vacate from nI (the i,j pair) !ExcitMat(2,*) are the orbitals to occupy in nJ (the a,b pair) (not the index, but the actual orbital) !**However, when the excitmat is returned, all elements refer to ORBITALS, NOT INDICES.** !IC should be 1 or 2, depending on whether it is a double or single excitation !Single excitations should just have ExcitMat(1,1) and ExcitMat(2,1) with orbital !information. !The algorithm could be improved for double excitations by only searching through the !determinant once, reducing it from an O[2N] to O[N] operation, though would be a little !more fiddly... ! [W.D. 11.12.2017]: ! never thought to touch this part of the code ever.. but we need triple excitations ! now too.. so adapt this functionality here.., since this function is ! unfortunately called in too many parts of the code.. module excit_mod use CalcData, only: TNEWEXCITATIONS use SystemData, only: BasisFN, tFixLz, nEl use constants, only: int64 use lattice_mod, only: sort_unique use sym_mod, only: lChkSym, GetLz, getsym use util_mod, only: NECI_ICOPY, stop_all better_implicit_none private public :: FindExcitDet, GETEXCITATION, GENEXCIT, isvaliddet contains SUBROUTINE FindExcitDet(ExcitMat, nI, IC, TParity) integer, intent(in) :: ic integer, intent(inout) :: ExcitMat(2, ic) integer, intent(inout) :: nI(nel) logical, intent(out) :: tParity #ifdef DEBUG_ character(*), parameter :: this_routine = "FindExcitDet" #endif integer :: i, k, pos_moved integer :: src(ic), sort_orbs(ic), sort_elecs(ic) ! adapt this for double excitations now.. #ifdef DEBUG_ if (IC < 0 .or. ic > 3) then call stop_all(this_routine, "wrong ic!") end if #endif if (ic == 3 .or. ic == 2) then !Ensure i<j and a<b ExcitMat(1, :) = sort_unique(ExcitMat(1, :)) ExcitMat(2, :) = sort_unique(ExcitMat(2, :)) end if sort_elecs = ExcitMat(1, :) ! Return Excitmat with orbitals, rather than indices being specified. ExcitMat(1, :) = nI(sort_elecs) ! this is the same functionality as in make_double.. but much more ! involved here.. so just take the core from make double and others.. ! look there for the code! src = nI(sort_elecs) sort_orbs = ExcitMat(2, :) ! reshuffle the orbitals.. if (ic > 1) then ! or check it individually: if (src(2) < sort_orbs(1)) then ! then i hops over j: sort_elecs(2) = sort_elecs(2) - 1 end if if (ic == 3) then if (src(3) < sort_orbs(1)) then ! then i hops over k ! (note: this also implies that j hops over k, but treat that ! seperately below, to also cover the case, where this if here ! is not fullfilled!) sort_elecs(3) = sort_elecs(3) - 1 end if if (src(3) < sort_orbs(2)) then ! then j hops over k sort_elecs(3) = sort_elecs(3) - 1 end if end if end if pos_moved = 0 !This keeps track of how far the common orbitals have moved. do k = 1, ic if (src(k) < sort_orbs(k)) then if (sort_elecs(k) == nel) then ! this can only happen for k == 3 i = nel + 1 nI(nel) = sort_orbs(k) else do i = sort_elecs(k) + 1, nel if (sort_orbs(k) < nI(i)) then nI(i - 1) = sort_orbs(k) exit else nI(i - 1) = nI(i) end if end do if (i == nel + 1) then nI(nel) = sort_orbs(k) end if end if else if (sort_elecs(k) == 1) then i = 0 nI(1) = sort_orbs(k) else do i = sort_elecs(k) - 1, 1, -1 if (sort_orbs(k) > nI(i)) then nI(i + 1) = sort_orbs(k) exit else nI(i + 1) = nI(i) end if end do if (i == 0) then nI(1) = sort_orbs(k) end if end if end if pos_moved = pos_moved + sort_elecs(k) - i + 1 end do tParity = btest(pos_moved, 0) END SUBROUTINE FindExcitDet logical pure function isvaliddet(det, nel) integer, intent(in) :: nel integer, intent(in) :: det(nel) integer i if (det(1) < 1) then isvaliddet = .false. return end if do i = 2, nel if (det(i - 1) >= det(i)) then isvaliddet = .false. return end if end do isvaliddet = .true. end !.. Get the orbitals which are excited in going from I to J !.. EX(1,*) are in I, and EX(2,*) are in J !.. TSIGN is set to the parity of the permutations required to line up the orbitals !.. TRUE means ODD. !.. If there are too many excitations to fit, then we put -excitlevel in EX(1,1) and EX(2,1) ! EX(1,1) is the max number of excitations (passed in as a parameter) SUBROUTINE GETEXCITATION(NI, NJ, NEL, EX, TSIGN) INTEGER NEL, NI(NEL), NJ(NEL), EX(2, *) INTEGER I, J, IPAR INTEGER IC1, IC2 INTEGER iMaxExcit LOGICAL TSIGN iMaxExcit = EX(1, 1) EX(1:2, 1:iMaxExcit) = 0 IC1 = 0 IC2 = 0 I = 1 J = 1 IPAR = 0 ! CALL WRITEDET(6,NI,NEL,.TRUE.) ! CALL WRITEDET(6,NJ,NEL,.TRUE.) DO WHILE (I <= NEL .AND. J <= NEL) !.. Differences from I to J ! WRITE(stdout,*) "GE",I,J DO WHILE (I <= NEL) if (NI(I) >= NJ(J)) exit IC1 = IC1 + 1 IF (IC1 <= iMaxExcit) THEN EX(1, IC1) = NI(I) IPAR = IPAR + I END IF I = I + 1 END DO !.. Differences from J to I DO WHILE (I <= NEL .AND. J <= NEL) if (NI(I) <= NJ(J)) exit IC2 = IC2 + 1 IF (IC2 <= iMaxExcit) THEN EX(2, IC2) = NJ(J) IPAR = IPAR + J END IF J = J + 1 END DO IF (I <= NEL .AND. J <= NEL) then if (NI(I) == NJ(J)) then I = I + 1 J = J + 1 end if END IF END DO !.. Deal with remaining I DO WHILE (I <= NEL) IC1 = IC1 + 1 IF (IC1 <= iMaxExcit) THEN IPAR = IPAR + I EX(1, IC1) = NI(I) END IF I = I + 1 END DO !.. Deal with remaining J DO WHILE (J <= NEL) IC2 = IC2 + 1 IF (IC2 <= iMaxExcit) THEN EX(2, IC2) = NJ(J) IPAR = IPAR + J END IF J = J + 1 END DO IF (iC1 > iMaxExcit) THEN !.. we actually needed more space. Just list the excitation counts (-ve) DO i = 1, iMaxExcit IF (i == 1) THEN EX(1, 1) = -iC1 EX(2, 1) = -iC2 ELSE EX(1, i) = 0 EX(2, i) = 0 END IF END DO ELSEIF (iC1 == 0) THEN EX(1, 1) = 0 EX(2, 1) = 0 END IF TSIGN = BTEST(IPAR, 0) END ! !.. Generate excitations of order at most NORDER from NI (excluding NI ! !itself) in order ! !.. ICLIST is the list of orders of the excitations ! !.. NMIN is the minimum level of excitation ! !.. IF NORDER=0, we SET NORDER=NEL ! !.. THis does not use the excitation generators, but enumerates all possible !.. determinants within double excitations, which will end up fairly inefficient. SUBROUTINE GENEXCIT(NI, NORDER, NBASIS, NEL, LIST, ICLIST, NLIST, NMIN, G1, TSYM, NBASISMAX, TCOUNT) integer, intent(in) :: NEL, NI(NEL), NORDER, NBASIS, LIST(NEL, *), ICLIST(*) INTEGER NEXCIT(NEL), NLIST, nBasisMax(5, *) TYPE(BASISFN) ISYM INTEGER NO LOGICAL TSYM, TCOUNT INTEGER NMIN type(BasisFN) G1(*) integer(int64) STORE(6) INTEGER ICOUNT, ILEVEL character(*), parameter :: t_r = "GENEXCIT" NO = NORDER IF (NO == 0) NO = NEL IF (TSYM) CALL GETSYM(NI, NEL, G1, NBASISMAX, ISYM) IF (TNEWEXCITATIONS .AND. NORDER <= 2) THEN ! Here the non-working routine `SYMSETUPEXCITS` was called. call stop_all(t_r, "Should never be here") ELSE NLIST = 1 CALL GENEXCIT_R(NI, NO, NEL, 1, NBASIS, LIST, ICLIST, NLIST, NEXCIT, NO, 1, NMIN, G1, ISYM, TSYM, NBASISMAX, TCOUNT) NLIST = NLIST - 1 END IF END !.. AT 29/1/04 - Looks like this won't scale very well to lots of !electrons !.. as there will be very few which are within NORDER excitations !of !.. our original det. (Or for that matter a large basis) !.. Recursively go through each electron ( we're on NELEC), filling !LIST. !.. with up to NORDER excitations. !.. NEXCIT is the determinant being constructed. !.. NLEFT is the number of possible excitations left !.. NSTARTFN is the basis fn to start with for this electron RECURSIVE SUBROUTINE GENEXCIT_R(NI, NORDER, NEL, NELEC, NBASIS, LIST, ICLIST, & NLISTPOS, NEXCIT, NLEFT, NSTARTFN, NMIN, G1, ISYM, TSYM, NBASISMAX, TCOUNT) INTEGER NEL, NELEC, NORDER, NLISTPOS, NLEFT, NBASIS, NSTARTFN, NNLEFT INTEGER NI(NEL), NEXCIT(NEL), LIST(NEL, *), ICLIST(*) INTEGER I, J, NMIN, NMAXEX, NExcitMl LOGICAL LISINOLD, LSYM, TSYM, TCOUNT, LZSYM TYPE(BASISFN) G1(NBASIS), ISYM, ISYM2 INTEGER nBasisMax(5, *) !.. NMAXEX is the maximum number of excitations we're allowed to have !left NMAXEX = NORDER - NMIN !.. I is the new basis fn for electron NELEC !.. We see if it's in the original determinant !.. we need to leave at least NEL-NELEC basis fns for the following !electrons DO I = NSTARTFN, NBASIS - (NEL - NELEC) LISINOLD = .FALSE. DO J = 1, NEL IF (NI(J) == I) LISINOLD = .TRUE. END DO NEXCIT(NELEC) = I NNLEFT = NLEFT IF (.NOT. LISINOLD) NNLEFT = NNLEFT - 1 !.. NNLEFT is the number of excitations left !.. check to see if we're actually exciting an electron, and if we've !any !.. spare excitations left !.. if we've allocated the last electron, we need to see if the det !.. is allowed, and if so, store it IF (NELEC == NEL) THEN !.. if we've excited at least one elec IF (NNLEFT <= NMAXEX .AND. NNLEFT >= 0) THEN !.. we check whether we're allowed this excitation owing to sym ! CALL WRITEDET(6,NEXCIT,NEL,.TRUE.) IF (TSYM) THEN CALL GETSYM(NEXCIT, NEL, G1, NBASISMAX, ISYM2) LSYM = LCHKSYM(ISYM, ISYM2) ELSE LSYM = .TRUE. END IF !We also want to check Lz symmetry IF (tFixLz) THEN CALL GetLz(NEXCIT, NEL, NExcitMl) IF (NExcitMl == (ISYM%Ml)) THEN LZSYM = .true. ELSE LZSYM = .false. END IF ELSE LZSYM = .true. END IF ! WRITE(stdout,*) "ISym:",ISYM ! WRITE(stdout,*) "ISym2",ISYM2 ! WRITE(stdout,*) "LSYM",LSYM IF (LSYM .and. LZSYM) THEN IF (.NOT. TCOUNT) THEN CALL NECI_ICOPY(NEL, NEXCIT, 1, LIST(1:NEL, NLISTPOS), 1) ICLIST(NLISTPOS) = NORDER - NNLEFT END IF NLISTPOS = NLISTPOS + 1 END IF END IF ELSEIF (NNLEFT >= 0) THEN !.. we start the next electron on the basis fn after this one CALL GENEXCIT_R(NI, NORDER, NEL, NELEC + 1, NBASIS, LIST, ICLIST, & NLISTPOS, NEXCIT, NNLEFT, I + 1, NMIN, G1, ISYM, TSYM, NBASISMAX, TCOUNT) END IF END DO END end module