--- src/constr_cell_relax.F     2020-08-25 23:27:21.000000000 +0800
+++ ../vasp.6.1.2.ext/src/constr_cell_relax.F   2020-12-02 09:53:37.541195944 +0800
@@ -27,17 +27,47 @@
       SUBROUTINE CONSTR_CELL_RELAX(FCELL)
       USE prec
       REAL(q) FCELL(3,3)
+      INTEGER FIXCELL(3,3) ! added by Mu
+      LOGICAL FCEXIST   !added by Mu
+      INTEGER  I,J,IREADFIX  ! added by Mu
+      SAVE FIXCELL,IREADFIX  ! added by Mu, before DATA
+      DATA IREADFIX /0/  ! added by Mu, 0-read in ,1- not read in
+      DATA FIXCELL /3*1,3*1,3*1/

 !     just one simple example
-!     relaxation in x directions only
-!      SAVE=FCELL(1,1)
-!      FCELL=0   ! F90 style: set the whole array to zero
-!      FCELL(1,1)=SAVE
-!     relaxation in z direction only
+!     relaxation in z directions only
 !      SAVE=FCELL(3,3)
 !      FCELL=0   ! F90 style: set the whole array to zero
 !      FCELL(3,3)=SAVE

+!  added by Mu
+      IF(IREADFIX==0) THEN
+        INQUIRE(file="FIXCELLCAR",exist=FCEXIST)
+        IF(FCEXIST) THEN
+          OPEN(unit=1983,file="FIXCELLCAR",status="old")
+            DO I=1,3
+                  READ(1983,*) (FIXCELL(J,I),J=1,3)
+            END DO
+          CLOSE(1983)
+          WRITE(*,*) "The Matrix for Fixing Cell as Follows:"
+          DO I=1,3
+            WRITE(*,*) (FIXCELL(J,I),J=1,3)
+          END DO
+          WRITE(*,*) "End of Matrix for Fixing Cell."
+          IREADFIX=2
+        ELSE
+          IREADFIX=1
+        END IF
+      END IF
+      IF(IREADFIX==2) THEN
+          DO I=1,3
+            DO J=1,3
+                IF(FIXCELL(J,I) == 0) FCELL(J,I)=0.0
+            END DO
+          END DO
+      END IF
+!!!!!!!!!!!  end , added by MU
+
       RETURN
       END SUBROUTINE
      END SUBROUTINE

1 1 0
1 1 0
0 0 0

--- ../vtstcode-180/neb.F       2012-07-13 06:18:54.000000000 +0800
+++ src/neb.F   2021-03-01 11:05:21.772776669 +0800
@@ -79,6 +79,12 @@
       REAL(q) :: strainA(3,3),strainB(3,3)
       REAL(q) :: strain_next(3,3),strain_prev(3,3)
       REAL(q) :: displacement, dR
+      INTEGER FIXCELL(3,3) ! added by Mu
+      LOGICAL FCEXIST   !added by Mu
+      INTEGER  IREADFIX  ! added by Mu
+      SAVE FIXCELL,IREADFIX  ! added by Mu, before DATA
+      DATA IREADFIX /0/  ! added by Mu, 0-read in ,1- not read in
+      DATA FIXCELL /3*1,3*1,3*1/

       optflag = .TRUE.
       IF (images==0) GOTO 9999
@@ -231,9 +237,37 @@
         !  WRITE(iu6,*) "NEBCELL: stress dot A"
         !  WRITE(iu6,'(3F13.5)') stress
         !ENDIF
+        !  added by Mu
+      IF(IREADFIX==0) THEN
+        INQUIRE(file="FIXCELLCAR",exist=FCEXIST)
+        IF(FCEXIST) THEN
+          OPEN(unit=1983,file="FIXCELLCAR",status="old")
+            DO I=1,3
+                  READ(1983,*) (FIXCELL(J,I),J=1,3)
+            END DO
+          CLOSE(1983)
+          WRITE(*,*) "The Matrix for Fixing Cell as Follows:"
+          DO I=1,3
+            WRITE(*,*) (FIXCELL(J,I),J=1,3)
+          END DO
+          WRITE(*,*) "End of Matrix for Fixing Cell."
+          IREADFIX=2
+        ELSE
+          IREADFIX=1
+        END IF
+      END IF
+      IF(IREADFIX==2) THEN
+          DO I=1,3
+            DO J=1,3
+                IF(FIXCELL(J,I) == 0) stress(J,I)=0._q
+            END DO
+          END DO
+      END IF
+        !!!!!!!!!!!  end , added by MU
         stress(2,1)=0._q
         stress(3,1)=0._q
         stress(3,2)=0._q
+
         ! convert normailized stress back to stress tensor
         CALL sdotB(stress,hinv)
         ! put everything in a big vector