c---------------------------------------------------------------------
c-----------------------------------------------------------------
      subroutine tnp1_respa_step1_
c Applying Nose-Poincare algorithm - step 1 to vel for RESPA
c JPSJ 70 75 (2001) S. Nose
c
c d_t is not updated here
c
      implicit real*8 (a-h,o-z)
      include 'DIMENSIONS'
      include 'COMMON.CONTROL'
      include 'COMMON.VAR'
      include 'COMMON.MD'
      include 'COMMON.CHAIN'
      include 'COMMON.DERIV'
      include 'COMMON.GEO'
      include 'COMMON.LOCAL'
      include 'COMMON.INTERACT'
      include 'COMMON.IOUNITS'
      include 'COMMON.NAMES'
      double precision adt,adt2,tmp
        
      tmp=1+pi_np/(2*Q_np)*0.5*d_time
      s12_np=s_np*tmp**2
      pistar=pi_np/tmp
      s12_dt=d_time/s12_np
      d_time_s12=d_time*0.5*s12_np

      do j=1,3
        d_t_old(j,0)=d_t_old(j,0)+d_a(j,0)*d_time_s12
      enddo
      do i=nnt,nct-1	
        do j=1,3    
          d_t_old(j,i)=d_t_old(j,i)+d_a(j,i)*d_time_s12
        enddo
      enddo
      do i=nnt,nct
        if (itype(i).ne.10) then
          inres=i+nres
          do j=1,3    
           d_t_old(j,inres)=d_t_old(j,inres)+d_a(j,inres)*d_time_s12
          enddo
        endif      
      enddo 
      return
      end