diff --git a/pyxtal/interface/latte_calculator.py b/pyxtal/interface/latte_calculator.py
new file mode 100644
index 00000000..3596f37c
--- /dev/null
+++ b/pyxtal/interface/latte_calculator.py
@@ -0,0 +1,316 @@
+from ase.io import read, write
+from ase.optimize import FIRE
+from ase.constraints import UnitCellFilter
+from ase.calculators.calculator import Calculator, all_changes
+
+from collections import Counter
+from pathlib import Path
+import numpy as np
+import os
+import subprocess
+import re
+
+# ===================== 1. LATTE Calculator =====================
+
+class LATTECalculator(Calculator):
+    """
+    Minimal ASE calculator that:
+       1) writes bl/inputblock.dat
+       2) runs LATTE
+       3) reads energy, stress, forces from
+              latte.log
+              lastsystem.cfg  (final frame only)
+
+    Requirements in workdir:
+       ./LATTE_DOUBLE
+       TBparam/control.in
+       MDcontroller
+       bl/ (auto-created)
+    """
+
+    implemented_properties = ["energy", "forces", "stress"]
+    
+    def __init__(self, exe="./LATTE_DOUBLE", workdir=".", timeout=3600, **kwargs):
+        super().__init__(**kwargs)
+        self.workdir = os.path.abspath(workdir)
+        self.exe = os.path.abspath(os.path.join(self.workdir, exe))
+        self.timeout = timeout
+        self.logfile = os.path.join(self.workdir, "latte.log")
+        self.cfgfile = os.path.join(self.workdir, "lastsystem.cfg")
+        
+    def calculation_required(self, atoms, properties):
+        return True
+        
+    def calculate(self, atoms=None, properties=("energy",), system_changes=all_changes):
+        if atoms is None:
+            atoms = self.atoms
+        else:
+            self.atoms = atoms.copy()
+
+        # clear previous results
+        self.results = {}
+
+        # write input for *current* geometry
+        self._write_inputblock(self.atoms)
+        self._set_single_point_mode()   # RELAX=0 in control.in
+
+        # run LATTE and parse outputs
+        self._run_latte()
+
+        E = self._read_energy_from_log()
+        F = self._read_forces_from_cfg()
+        S = self._read_stress_from_log()
+
+        self.results["energy"] = E
+        self.results["forces"] = F
+        if S is not None:
+            self.results["stress"] = S
+
+    # Write inputblock.dat
+    def _write_inputblock(self, atoms):
+        bl = os.path.join(self.workdir, "bl")
+        os.makedirs(bl, exist_ok=True)
+        fpath = os.path.join(bl, "inputblock.dat")
+
+        cell = atoms.cell.array
+        pos = atoms.get_positions()
+        syms = atoms.get_chemical_symbols()
+
+        with open(fpath, "w") as f:
+            f.write(f"{len(atoms)}\n")
+            for v in cell:
+                f.write(f"{v[0]:.10f} {v[1]:.10f} {v[2]:.10f}\n")
+            for s, r in zip(syms, pos):
+                f.write(f"{s} {r[0]:.10f} {r[1]:.10f} {r[2]:.10f}\n")
+
+    # Force single-point mode in control.in
+    def _set_single_point_mode(self):
+        cpath = os.path.join(self.workdir, "TBparam", "control.in")
+        if not os.path.exists(cpath):
+            print("WARNING: No control.in found.")
+            return
+
+        lines = open(cpath).read().splitlines()
+        new = []
+        updated_relax = False
+
+        for line in lines:
+            if line.strip().startswith("RELAX"):
+                updated_relax = True
+                new.append("RELAX= 0 RELAXTYPE= SD MAXITER= 10 RLXFTOL= 0.1\n")
+            else:
+                new.append(line + "\n")
+
+        if not updated_relax:
+            new.append("\nRELAX= 0 RELAXTYPE= SD MAXITER= 10 RLXFTOL= 0.1\n")
+
+        open(cpath, "w").write("".join(new))
+
+    # Run LATTE
+    def _run_latte(self):
+        with open(self.logfile, "w") as f:
+            subprocess.run(
+                [self.exe],
+                cwd=self.workdir,
+                stdout=f, stderr=subprocess.STDOUT,
+                timeout=self.timeout, check=True
+            )
+
+    # Read total energy from latte.log
+    def _read_energy_from_log(self):
+        lines = open(self.logfile).read().splitlines()
+        E = None
+        pattern = re.compile(r"FREE ENERGY\s*=\s*([-0-9.Ee]+)")
+        for l in lines:
+            m = pattern.search(l)
+            if m:
+                E = float(m.group(1))
+        if E is None:
+            raise RuntimeError("Energy not found in log!")
+        return E
+
+    # Read stress tensor from latte.log (GPa → eV/A³)
+    def _read_stress_from_log(self):
+        lines = open(self.logfile).read().splitlines()
+        S = None
+        for i, l in enumerate(lines):
+            if "Stress tensor (GPa)" in l:
+                m = []
+                for j in range(1, 4):
+                    parts = lines[i+j].replace("#","").split()
+                    m.append([float(x) for x in parts[:3]])
+                S = np.array(m)
+                break
+
+        if S is None:
+            return None
+
+        # convert GPa → eV/ų and flip sign (LATTE → ASE convention)
+        conv = 0.00625
+        return -(S*conv)
+
+    # Read the LAST FRAME from lastsystem.cfg
+    def _read_forces_from_cfg(self):
+        if not os.path.exists(self.cfgfile):
+            raise RuntimeError("lastsystem.cfg not found")
+
+        lines = open(self.cfgfile).read().splitlines()
+
+        # number of atoms
+        natoms = None
+        for l in lines:
+            if "Number of particles" in l:
+                natoms = int(l.split("=")[1])
+                break
+
+        if natoms is None:
+            raise RuntimeError("Could not find 'Number of particles' in lastsystem.cfg")
+
+        # H0 matrix
+        H = np.zeros((3, 3))
+        for l in lines:
+            if "H0(" in l:
+                tmp = l.replace("=", " ").replace("A", "").split()
+                ij = tmp[0][3:-1]
+                i, j = ij.split(",")
+                H[int(i) - 1, int(j) - 1] = float(tmp[1])
+
+        # collect all numeric atom-lines (≥7 floats)
+        all_atoms = []
+        for l in lines:
+            p = l.split()
+            if len(p) < 7:
+                continue
+            try:
+                nums = [float(x) for x in p[:7]]
+                all_atoms.append(nums)
+            except ValueError:
+                continue
+
+        if len(all_atoms) < natoms:
+            raise RuntimeError("Not enough atom lines found in lastsystem.cfg")
+
+        # last natoms rows = final forces
+        block = all_atoms[-natoms:]
+
+        frac = np.array([b[:3] for b in block])
+        forces = np.array([b[3:6] for b in block])
+
+        coords_cart = frac @ H  # not used but kept for completeness
+
+        return forces
+
+# ===================== 2. Reorder CIF & fix formula =====================
+
+def reorder_cif_and_fix_formula(infile, outfile, desired_order=("O", "H", "C")):
+    """
+    Read CIF, reorder atoms by desired_order, write new CIF,
+    and fix _chemical_formula_sum line. Returns reordered Atoms.
+    """
+    atoms = read(infile)
+
+    # Reorder atoms
+    symbols = np.array(atoms.get_chemical_symbols())
+    indices = []
+    for el in desired_order:
+        idx = np.where(symbols == el)[0]
+        indices.extend(idx.tolist())
+    atoms_reordered = atoms[indices]
+
+    # Write reordered CIF
+    write(outfile, atoms_reordered, format="cif")
+
+    # Count elements
+    counts = Counter(atoms_reordered.get_chemical_symbols())
+    parts = []
+    for el in desired_order:
+        if el in counts:
+            n = counts[el]
+            parts.append(f"{el}{n}" if n != 1 else el)
+    custom_formula = " ".join(parts)
+
+    # Patch _chemical_formula_sum
+    text = Path(outfile).read_text()
+    lines = text.splitlines()
+
+    new_lines = []
+    formula_found = False
+    for line in lines:
+        if line.lower().startswith("_chemical_formula_sum"):
+            new_lines.append(f"_chemical_formula_sum    '{custom_formula}'")
+            formula_found = True
+        else:
+            new_lines.append(line)
+
+    if not formula_found:
+        inserted = []
+        inserted_flag = False
+        for line in new_lines:
+            inserted.append(line)
+            if (not inserted_flag) and line.lower().startswith("data_"):
+                inserted.append(f"_chemical_formula_sum    '{custom_formula}'")
+                inserted_flag = True
+        new_lines = inserted
+
+    Path(outfile).write_text("\n".join(new_lines))
+
+    print("Wrote reordered CIF to:", outfile)
+    print("Formula set to:", custom_formula)
+    return atoms_reordered
+
+# ===================== 3. Stress logger =====================
+
+def log_stress(atoms, filename="stress_log.txt"):
+    """
+    Append latest stress tensor from atoms.calc.results["stress"]
+    to filename without forcing a new LATTE evaluation.
+    """
+    calc = atoms.calc
+    S = calc.results.get("stress", None)
+    if S is None:
+        # fall back to ASE call if needed (this will trigger a calc)
+        S = atoms.get_stress(voigt=False)
+
+    S = np.array(S)
+
+    first_time = not os.path.exists(filename)
+    with open(filename, "a") as f:
+        if first_time:
+            f.write("# xx yy zz yz xz xy\n")
+        if S.shape == (3, 3):
+            xx, yy, zz = S[0, 0], S[1, 1], S[2, 2]
+            yz, xz, xy = S[1, 2], S[0, 2], S[0, 1]
+            f.write(f"{xx: .6f} {yy: .6f} {zz: .6f} {yz: .6f} {xz: .6f} {xy: .6f}\n")
+        else:
+            # assume already 6-component
+            f.write(" ".join(f"{x: .6f}" for x in S) + "\n")
+
+# ===================== 4. Main workflow =====================
+
+if __name__ == "__main__":
+    # --- user settings ---
+    infile = "bddc_exp.cif"               # Original CIF
+    rearranged_cif = "rearranged_bddc.cif"  # Reordered output CIF
+    latte_workdir = "."               # Folder with LATTE_DOUBLE, TBparam, MDcontroller
+
+    # 1) Reorder CIF + fix formula, get reordered Atoms
+    desired_order = ("O", "H", "C")   #(you can see the order through running with original one for 1 step and observe from "lastsystem.cfg")
+    atoms = reorder_cif_and_fix_formula(infile, rearranged_cif, desired_order)
+
+    # 2) Attach LATTE calculator
+    calc = LATTECalculator(exe="./LATTE_DOUBLE", workdir=latte_workdir)
+    atoms.set_calculator(calc)
+
+    # 3) Cell + atomic relaxation with FIRE
+    ucf = UnitCellFilter(atoms)
+    opt = FIRE(ucf, dt=0.2, maxmove=0.2, logfile="latte_opt.log")
+
+    # Attach stress logger (uses closure over 'atoms')
+    opt.attach(lambda: log_stress(atoms, filename="stress_log.txt"), interval=10)
+
+    opt.run(fmax=0.1)
+
+    # 4) Save relaxed structure
+    write("Relaxed_structure.cif", atoms)
+    print("Relaxed structure written to Relaxed_structure.cif")
+