+C-----------------------------------------------------------------------
+C-----------------------------------------------------------
+C This subroutine is to mimic the histone like structure but as well can be
+C utilizet to nanostructures (infinit) small modification has to be used to
+C make it finite (z gradient at the ends has to be changes as well as the x,y
+C gradient has to be modified at the ends
+C The energy function is Kihara potential
+C E=4esp*((sigma/(r-r0))^12 - (sigma/(r-r0))^6)
+C 4eps is depth of well sigma is r_minimum r is distance from center of tube
+C and r0 is the excluded size of nanotube (can be set to 0 if we want just a
+C simple Kihara potential
+ subroutine calctube(Etube)
+ implicit real*8 (a-h,o-z)
+ include 'DIMENSIONS'
+ include 'COMMON.GEO'
+ include 'COMMON.VAR'
+ include 'COMMON.LOCAL'
+ include 'COMMON.CHAIN'
+ include 'COMMON.DERIV'
+ include 'COMMON.NAMES'
+ include 'COMMON.INTERACT'
+ include 'COMMON.IOUNITS'
+ include 'COMMON.CALC'
+ include 'COMMON.CONTROL'
+ include 'COMMON.SPLITELE'
+ include 'COMMON.SBRIDGE'
+ double precision tub_r,vectube(3),enetube(maxres*2)
+ Etube=0.0d0
+ do i=1,2*nres
+ enetube(i)=0.0d0
+ enddo
+C first we calculate the distance from tube center
+C first sugare-phosphate group for NARES this would be peptide group
+C for UNRES
+ do i=1,nres
+C lets ommit dummy atoms for now
+ if ((itype(i).eq.ntyp1).or.(itype(i+1).eq.ntyp1)) cycle
+C now calculate distance from center of tube and direction vectors
+ vectube(1)=(c(1,i)+c(1,i+1))/2.0d0-tubecenter(1)
+ vectube(2)=(c(2,i)+c(2,i+1))/2.0d0-tubecenter(2)
+C print *,"x",(c(1,i)+c(1,i+1))/2.0d0,tubecenter(1)
+C print *,"y",(c(2,i)+c(2,i+1))/2.0d0,tubecenter(2)
+
+C as the tube is infinity we do not calculate the Z-vector use of Z
+C as chosen axis
+ vectube(3)=0.0d0
+C now calculte the distance
+ tub_r=dsqrt(vectube(1)**2+vectube(2)**2+vectube(3)**2)
+C now normalize vector
+ vectube(1)=vectube(1)/tub_r
+ vectube(2)=vectube(2)/tub_r
+C calculte rdiffrence between r and r0
+ rdiff=tub_r-tubeR0
+C and its 6 power
+ rdiff6=rdiff**6.0d0
+C for vectorization reasons we will sumup at the end to avoid depenence of previous
+ enetube(i)=pep_aa_tube/rdiff6**2.0d0-pep_bb_tube/rdiff6
+C write(iout,*) "TU13",i,rdiff6,enetube(i)
+C print *,rdiff,rdiff6,pep_aa_tube
+C pep_aa_tube and pep_bb_tube are precomputed values A=4eps*sigma^12 B=4eps*sigma^6
+C now we calculate gradient
+ fac=(-12.0d0*pep_aa_tube/rdiff6+
+ & 6.0d0*pep_bb_tube)/rdiff6/rdiff
+C write(iout,'(a5,i4,f12.1,3f12.5)') "TU13",i,rdiff6,enetube(i),
+C &rdiff,fac
+
+C now direction of gg_tube vector
+ do j=1,3
+ gg_tube(j,i-1)=gg_tube(j,i-1)+vectube(j)*fac/2.0d0
+ gg_tube(j,i)=gg_tube(j,i)+vectube(j)*fac/2.0d0
+ enddo
+ enddo
+C basically thats all code now we split for side-chains (REMEMBER to sum up at the END)
+ do i=1,nres
+C Lets not jump over memory as we use many times iti
+ iti=itype(i)
+C lets ommit dummy atoms for now
+ if ((iti.eq.ntyp1)
+C in UNRES uncomment the line below as GLY has no side-chain...
+C .or.(iti.eq.10)
+ & ) cycle
+ vectube(1)=c(1,i+nres)-tubecenter(1)
+ vectube(2)=c(2,i+nres)-tubecenter(2)
+
+C as the tube is infinity we do not calculate the Z-vector use of Z
+C as chosen axis
+ vectube(3)=0.0d0
+C now calculte the distance
+ tub_r=dsqrt(vectube(1)**2+vectube(2)**2+vectube(3)**2)
+C now normalize vector
+ vectube(1)=vectube(1)/tub_r
+ vectube(2)=vectube(2)/tub_r
+C calculte rdiffrence between r and r0
+ rdiff=tub_r-tubeR0
+C and its 6 power
+ rdiff6=rdiff**6.0d0
+C for vectorization reasons we will sumup at the end to avoid depenence of previous
+ sc_aa_tube=sc_aa_tube_par(iti)
+ sc_bb_tube=sc_bb_tube_par(iti)
+ enetube(i+nres)=sc_aa_tube/rdiff6**2.0d0-sc_bb_tube/rdiff6
+C pep_aa_tube and pep_bb_tube are precomputed values A=4eps*sigma^12 B=4eps*sigma^6
+C now we calculate gradient
+ fac=-12.0d0*sc_aa_tube/rdiff6**2.0d0/rdiff+
+ & 6.0d0*sc_bb_tube/rdiff6/rdiff
+C now direction of gg_tube vector
+ do j=1,3
+ gg_tube_SC(j,i)=gg_tube_SC(j,i)+vectube(j)*fac
+ gg_tube(j,i-1)=gg_tube(j,i-1)+vectube(j)*fac
+ enddo
+ enddo
+ do i=1,2*nres
+ Etube=Etube+enetube(i)
+ enddo
+C print *,"ETUBE", etube
+ return
+ end
+C TO DO 1) add to total energy
+C 2) add to gradient summation
+C 3) add reading parameters (AND of course oppening of PARAM file)
+C 4) add reading the center of tube
+C 5) add COMMONs
+C 6) add to zerograd