pp-RPA

examples/molecule.H2

@@ -2,4 +2,4 @@
  2   1     1   0     0
 # Znuc   x            y           z
   H     0.           0.         0.
-  H     0.           0.         0.6
+  H     0.           0.         1.4

input/basis

@@ -1,9 +1,16 @@
-1   3
+1   6
-S   3   1.00
+S   4   1.00
-     38.3600000              0.0238090        
+    234.0000000              0.0025870        
-      5.7700000              0.1548910        
+     35.1600000              0.0195330        
-      1.2400000              0.4699870        
+      7.9890000              0.0909980        
+      2.2120000              0.2720500        
 S   1   1.00
-      0.2976000              1.0000000        
+      0.6669000              1.0000000        
+S   1   1.00
+      0.2089000              1.0000000        
 P   1   1.00
-      1.2750000              1.0000000 
+      3.0440000              1.0000000        
+P   1   1.00
+      0.7580000              1.0000000        
+D   1   1.00
+      1.9650000              1.0000000   

input/options

@@ -5,7 +5,7 @@
 # CC: maxSCF thresh   DIIS n_diis
       64     0.00001  F    1
 # CIS/TDHF/BSE: singlet triplet
-            T       F
+            T       T
 # GF: maxSCF thresh  DIIS n_diis renormalization
       64     0.00001 T    10      3 
 # GW: maxSCF thresh  DIIS n_diis COHSEX SOSEX BSE TDA G0W GW0 linearize eta

input/weight

@@ -1,9 +1,16 @@
-1   3
+1   6
-S   3   1.00
+S   4   1.00
-     38.3600000              0.0238090        
+    234.0000000              0.0025870        
-      5.7700000              0.1548910        
+     35.1600000              0.0195330        
-      1.2400000              0.4699870        
+      7.9890000              0.0909980        
+      2.2120000              0.2720500        
 S   1   1.00
-      0.2976000              1.0000000        
+      0.6669000              1.0000000        
+S   1   1.00
+      0.2089000              1.0000000        
 P   1   1.00
-      1.2750000              1.0000000 
+      3.0440000              1.0000000        
+P   1   1.00
+      0.7580000              1.0000000        
+D   1   1.00
+      1.9650000              1.0000000   

src/QuAcK/linear_response_B_pp.f90

@@ -39,14 +39,14 @@ subroutine linear_response_B_pp(ispin,dRPA,nBas,nC,nO,nV,nR,nOO,nVV,e,ERI,B_pp)
  
   ab = 0
   do a=nO+1,nBas-nR
-    do b=nO+1,nBas-nR
+   do b=a+1,nBas-nR
       ab = ab + 1
       ij = 0
       do i=nC+1,nO
-        do j=nC+1,nO
+       do j=i+1,nO
           ij = ij + 1
 
-          B_pp(ab,ij) = (1d0 + delta_spin)*ERI(a,b,i,j) - (1d0 - delta_dRPA)*ERI(a,b,j,j)
+          B_pp(ab,ij) = (1d0 + delta_spin)*ERI(a,b,i,j) - (1d0 - delta_dRPA)*ERI(a,b,j,i)
 
         enddo
       enddo

src/QuAcK/linear_response_C_pp.f90

@@ -16,6 +16,7 @@ subroutine linear_response_C_pp(ispin,dRPA,nBas,nC,nO,nV,nR,nOO,nVV,e,ERI,C_pp)
 
   double precision              :: delta_spin
   double precision              :: delta_dRPA
+  double precision              :: eF
   double precision,external     :: Kronecker_delta
 
   integer                       :: a,b,c,d,ab,cd
@@ -35,18 +36,20 @@ subroutine linear_response_C_pp(ispin,dRPA,nBas,nC,nO,nV,nR,nOO,nVV,e,ERI,C_pp)
   delta_dRPA = 0d0
   if(dRPA) delta_dRPA = 1d0
 
-! Build A matrix
+! Build C matrix
+ 
+  eF = e(nO) + e(nO+1)
 
   ab = 0
   do a=nO+1,nBas-nR
-    do b=nO+1,nBas-nR
+   do b=a+1,nBas-nR
       ab = ab + 1
       cd = 0
       do c=nO+1,nBas-nR
-        do d=nO+1,nBas-nR
+       do d=c+1,nBas-nR
           cd = cd + 1
 
-          C_pp(ab,cd) = (e(a) + e(b))*Kronecker_delta(a,c)*Kronecker_delta(b,d) & 
+          C_pp(ab,cd) = + (e(a) + e(b) - eF)*Kronecker_delta(a,c)*Kronecker_delta(b,d) & 
                         + (1d0 + delta_spin)*ERI(a,b,c,d) - (1d0 - delta_dRPA)*ERI(a,b,d,c)
 
         enddo

src/QuAcK/linear_response_D_pp.f90

@@ -14,6 +14,7 @@ subroutine linear_response_D_pp(ispin,dRPA,nBas,nC,nO,nV,nR,nOO,nVV,e,ERI,D_pp)
   
 ! Local variables
 
+  double precision              :: eF
   double precision              :: delta_spin
   double precision              :: delta_dRPA
   double precision,external     :: Kronecker_delta
@@ -35,18 +36,20 @@ subroutine linear_response_D_pp(ispin,dRPA,nBas,nC,nO,nV,nR,nOO,nVV,e,ERI,D_pp)
   delta_dRPA = 0d0
   if(dRPA) delta_dRPA = 1d0
 
-! Build A matrix
+! Build D matrix
+
+  eF = e(nO) + e(nO+1)
  
   ij = 0
   do i=nC+1,nO
-    do j=nC+1,nO
+   do j=i+1,nO
       ij = ij + 1
       kl = 0
       do k=nC+1,nO
-        do l=nC+1,nO
+       do l=k+1,nO
           kl = kl + 1
 
-          D_pp(ij,kl) = - (e(i) + e(j))*Kronecker_delta(i,k)*Kronecker_delta(j,l) & 
+          D_pp(ij,kl) = - (e(i) + e(j) - eF)*Kronecker_delta(i,k)*Kronecker_delta(j,l) & 
                         + (1d0 + delta_spin)*ERI(k,l,i,j) - (1d0 - delta_dRPA)*ERI(k,l,j,i)
 
         enddo

src/QuAcK/linear_response_pp.f90

@@ -1,6 +1,6 @@
 subroutine linear_response_pp(ispin,dRPA,TDA,BSE,nBas,nC,nO,nV,nR,nS,e,ERI,rho,Ec_ppRPA)
 
-! Compute the p-p channel of the linear response
+! Compute the p-p channel of the linear response: see Scueria et al. JCP 139, 104113 (2013)
 
   implicit none
   include 'parameters.h'
@@ -24,7 +24,14 @@ subroutine linear_response_pp(ispin,dRPA,TDA,BSE,nBas,nC,nO,nV,nR,nS,e,ERI,rho,E
   double precision,allocatable  :: C(:,:)
   double precision,allocatable  :: D(:,:)
   double precision,allocatable  :: M(:,:)
+  double precision,allocatable  :: Z(:,:)
   double precision,allocatable  :: w(:)
+  double precision,allocatable  :: w1(:)
+  double precision,allocatable  :: w2(:)
+  double precision,allocatable  :: X1(:,:)
+  double precision,allocatable  :: Y1(:,:)
+  double precision,allocatable  :: X2(:,:)
+  double precision,allocatable  :: Y2(:,:)
 
 ! Output variables
 
@@ -32,12 +39,13 @@ subroutine linear_response_pp(ispin,dRPA,TDA,BSE,nBas,nC,nO,nV,nR,nS,e,ERI,rho,E
 
 ! Useful quantities
 
-  nOO = nO*nO
+ nOO = nO*(nO-1)/2
-  nVV = nV*nV
+ nVV = nV*(nV-1)/2
 
 ! Memory allocation
 
-  allocate(B(nVV,nOO),C(nVV,nVV),D(nOO,nOO),M(nOO+nVV,nOO+nVV),w(nOO+nVV))
+  allocate(B(nVV,nOO),C(nVV,nVV),D(nOO,nOO),M(nOO+nVV,nOO+nVV),Z(nOO+nVV,nOO+nVV),w(nOO+nVV), &
+           w1(nVV),w2(nOO),X1(nVV,nVV),Y1(nVV,nOO),X2(nOO,nVV),Y2(nOO,nOO))
 
 ! Build B, C and D matrices for the pp channel
 
@@ -69,22 +77,33 @@ subroutine linear_response_pp(ispin,dRPA,TDA,BSE,nBas,nC,nO,nV,nR,nS,e,ERI,rho,E
 
 ! Diagonalize the p-h matrix
 
-  call diagonalize_matrix(nOO+nVV,M(:,:),w(:))
+  Z(:,:) = M(:,:)
+  call diagonalize_matrix(nOO+nVV,Z(:,:),w(:))
 
-! Build X+Y
+  write(*,*) 'pp-RPA excitation energies'
+  call matout(nOO+nVV,1,w(:))
+  write(*,*) 
 
-! XpY(1:nS,1:nS) = M(nS+1:2*nS,1:nS) + M(nS+1:2*nS,nS+1:2*nS)
+! Split the various quantities in p-p and h-h parts
 
-! print*,'X+Y'
+  w1(:) = w(nOO+1:nOO+nVV)
-! call matout(nS,nS,XpY)
+  w2(:) = w(1:nOO)
 
-  print*,'pp-RPA excitation energies'
+  X1(:,:) = Z(nOO+1:nOO+nVV,    1:nVV    )
-  call matout(nOO+nVV,1,w)
+  Y1(:,:) = Z(nOO+1:nOO+nVV,nVV+1:nOO+nVV)
+  X2(:,:) = Z(    1:nOO    ,    1:nVV    ) 
+  Y2(:,:) = Z(    1:nOO    ,nVV+1:nOO+nVV)
+
+  if(minval(w1(:)) < 0d0) call print_warning('You may have instabilities in pp-RPA!!')
+  if(maxval(w2(:)) > 0d0) call print_warning('You may have instabilities in pp-RPA!!')
 
 ! Compute the RPA correlation energy
 
-  Ec_ppRPA = 0.5d0*(sum(abs(w(:))) - trace_matrix(nVV,C(:,:)) - trace_matrix(nOO,D(:,:)))
+  Ec_ppRPA = 0.5d0*( sum(w1(:)) - sum(w2(:)) - trace_matrix(nVV,C(:,:)) - trace_matrix(nOO,D(:,:)) )
 
   print*,'Ec(pp-RPA) = ',Ec_ppRPA
+  print*,'Ec(pp-RPA) = ',0.5d0*( sum(abs(w(:))) - trace_matrix(nVV*nOO,M(:,:)))
+  print*,'Ec(pp-RPA) = ',+sum(w1(:)) - trace_matrix(nVV,C(:,:))
+  print*,'Ec(pp-RPA) = ',-sum(w2(:)) - trace_matrix(nOO,D(:,:))
 
 end subroutine linear_response_pp