(DENSITY-target)=
# DENSITY
```{tags} Quantum Mechanics
```

Retrieve electronic density information.



## <DENSITY

Retrieve electronic density on a set of grid points.

**Datatype:** `MDI_DOUBLE`  
**Quantity**: `3 * NDENSITY`  

 The engine sends the value of its electronic density on a set of grid points.  This command is intended to be used in conjuction with the [<NDENSITY](NDENSITY) and [<CDENSITY](CDENSITY) commands;  these three commands enable a driver to acquire the electronic density distribution of an engine in a grid representation.


### Examples


::::{tab-set}

:::{tab-item} Python
:sync: python

```python
import mdi
# connect to the engine
mdi_engine = mdi.MDI_Accept_Communicator()

# retrieve the number of grid points
mdi.MDI_Send_Command("<NDENSITY", mdi_engine)
ndensity = mdi.MDI_Recv(1, mdi.MDI_INT, mdi_engine)

# receive the electronic density on a set of grid points
mdi.MDI_Send_Command("<DENSITY", mdi_engine)
density = mdi.MDI_Recv(3*ndensity, mdi.MDI_DOUBLE, mdi_engine)

```
:::

:::{tab-item} Python (NumPy)
:sync: python (numpy)

```python
import mdi
import numpy as np

# connect to the engine
mdi_engine = mdi.MDI_Accept_Communicator()

# retrieve the number of grid points
mdi.MDI_Send_Command("<NDENSITY", mdi_engine)
ndensity = mdi.MDI_Recv(1, mdi.MDI_INT, mdi_engine)

# create a buffer to hold the electronic density values
density = np.zeros(3*ndensity, dtype=float)

# receive the electronic density on a set of grid points
mdi.MDI_Send_Command("<DENSITY", mdi_engine)
mdi.MDI_Recv(3*ndensity, mdi.MDI_DOUBLE, mdi_engine, buf=density)

```
:::

:::{tab-item} C++
:sync: cpp

```cpp
#include "mdi.h"
#include <vector>

// connect to the engine
MDI_Comm mdi_engine = MDI_Accept_Communicator();

// receive the Cartesian coordinates of the grid points
int ndensity;
MDI_Send_Command("<NDENSITY", mdi_engine);
MDI_Recv(&ndensity, 1, MDI_INT, mdi_engine);

// create a vector to hold the Cartesian coordinates of the grid points
std::vector<double> density(3*ndensity);

// receive the electronic density on a set of grid points
MDI_Send_Command("<DENSITY", mdi_engine);
MDI_Recv(density.data(), 3*ndensity, MDI_DOUBLE, mdi_engine);

```
:::

::::