app.py

# ===== Ultimate Quantum Chemistry Platform (Starter) =====
# Python 3.11 + Qiskit stable + Gradio + Plotly
import numpy as np
import plotly.graph_objects as go
import gradio as gr

from qiskit_nature.second_q.drivers import PySCFDriver
from qiskit_nature.second_q.problems import ElectronicStructureProblem
from qiskit_nature.second_q.mappers import JordanWignerMapper
from qiskit.algorithms.minimum_eigensolvers import VQE
from qiskit.algorithms.optimizers import COBYLA
from qiskit.circuit.library import TwoLocal
from qiskit.primitives import Estimator  # stable Qiskit 1.12

# ----------------------------
# Molecules Library
# ----------------------------
molecules = {
    "H2": {"atoms": ["H", "H"], "coords": [(0,0,0), (0,0,0.74)]},
    "LiH": {"atoms": ["Li", "H"], "coords": [(0,0,0), (0,0,1.6)]},
    "BeH2": {"atoms": ["Be","H","H"], "coords": [(0,0,0), (0,0,1.3), (0,0,-1.3)]}
}

# ----------------------------
# Quantum ground state energy
# ----------------------------
def compute_ground_state_energy(mol_name, bond_length):
    bond_length = float(bond_length)
    
    if mol_name == "H2":
        atom_str = f"H 0 0 0; H 0 0 {bond_length}"
    elif mol_name == "LiH":
        atom_str = f"Li 0 0 0; H 0 0 {bond_length}"
    elif mol_name == "BeH2":
        # symmetrically along z-axis
        atom_str = f"Be 0 0 0; H 0 0 {bond_length}; H 0 0 {-bond_length}"
    else:
        raise ValueError("Molecule not supported")
    
    driver = PySCFDriver(atom=atom_str, basis="sto3g")
    problem = ElectronicStructureProblem(driver)
    hamiltonian = problem.second_q_ops()[0]
    
    qubit_op = JordanWignerMapper().map(hamiltonian)
    
    ansatz = TwoLocal(qubit_op.num_qubits, "ry", "cz", reps=2)
    vqe = VQE(estimator=Estimator(), ansatz=ansatz, optimizer=COBYLA(maxiter=80))
    
    result = vqe.compute_minimum_eigenvalue(qubit_op)
    energy = result.eigenvalue.real
    return energy

# ----------------------------
# 3D molecule plot
# ----------------------------
def molecule_3d_plot(mol_name, bond_length):
    bond_length = float(bond_length)
    if mol_name == "H2":
        coords = [(0,0,0),(0,0,bond_length)]
    elif mol_name == "LiH":
        coords = [(0,0,0),(0,0,bond_length)]
    elif mol_name == "BeH2":
        coords = [(0,0,0),(0,0,bond_length),(0,0,-bond_length)]
    else:
        coords = []
    
    x, y, z = zip(*coords)
    fig = go.Figure()
    fig.add_trace(go.Scatter3d(
        x=x, y=y, z=z,
        mode="markers",
        marker=dict(size=8, color="red")
    ))
    fig.add_trace(go.Scatter3d(
        x=x, y=y, z=z,
        mode="lines",
        line=dict(color="blue", width=5)
    ))
    fig.update_layout(scene=dict(aspectmode="data"))
    return fig

# ----------------------------
# Energy curve precompute (for 0.4 - 2.0 Å)
# ----------------------------
bond_grid = np.linspace(0.4, 2.0, 12)
energy_curves = {}
for mol in molecules:
    energy_curves[mol] = [compute_ground_state_energy(mol, bl) for bl in bond_grid]

# ----------------------------
# Update UI
# ----------------------------
def update_ui(mol_name, bond_length):
    bond_length = float(bond_length)
    energy = compute_ground_state_energy(mol_name, bond_length)
    mol_fig = molecule_3d_plot(mol_name, bond_length)
    
    curve_fig = go.Figure()
    curve_fig.add_trace(go.Scatter(
        x=bond_grid, y=energy_curves[mol_name],
        mode="lines+markers",
        name="Energy Curve"
    ))
    curve_fig.add_trace(go.Scatter(
        x=[bond_length], y=[energy],
        mode="markers",
        marker=dict(size=12, color="green"),
        name="Current Energy"
    ))
    min_idx = int(np.argmin(energy_curves[mol_name]))
    curve_fig.add_trace(go.Scatter(
        x=[bond_grid[min_idx]], y=[energy_curves[mol_name][min_idx]],
        mode="markers",
        marker=dict(size=14, color="orange"),
        name="Equilibrium"
    ))
    curve_fig.update_layout(
        xaxis_title="Bond Length (Å)",
        yaxis_title="Energy (Hartree)"
    )
    
    text = f"Ground state energy: {energy:.6f} Hartree\nEquilibrium bond length ≈ {bond_grid[min_idx]:.2f} Å"
    return text, mol_fig, curve_fig

# ----------------------------
# Gradio App
# ----------------------------
with gr.Blocks() as demo:
    gr.Markdown("# 🧬 Ultimate Quantum Chemistry Platform")
    
    mol_dropdown = gr.Dropdown(list(molecules.keys()), value="H2", label="Select Molecule")
    bond_slider = gr.Slider(0.4, 2.0, value=0.74, step=0.01, label="Bond Length (Å)")
    
    energy_box = gr.Textbox(label="Energy", lines=2)
    mol_plot = gr.Plot(label="3D Molecule")
    curve_plot = gr.Plot(label="Energy Curve")
    
    mol_dropdown.change(update_ui, [mol_dropdown, bond_slider], [energy_box, mol_plot, curve_plot])
    bond_slider.change(update_ui, [mol_dropdown, bond_slider], [energy_box, mol_plot, curve_plot])

demo.launch()