Electronic – Wien bridge oscillator LTSPICE

Your opamp only has a gain of 1.
A wien bridge oscillator needs a gain of 3 to compensate for the attenuation of the RC network at the freqeuncy of oscillation.
Try adding the neccessary feedback resistors for G = 3. You would typically need some AGC (automatic gain control) in a real circuit, possibly here too.

EDIT - I just noticed the 3.01k resistor (R4) on the V+ pin of the opamp. What is this for?
It will certianly cause strange behaviour as the opamps supply voltage will vary according to how much current it draws.
To simplify things I would get rid of R3,R4,Q1 and V3. Just use V1 to supply 5V directly to the V+ pin (pin 7)
If you could update your diagram with the new version (with gain setting resistors, etc) it would help to be sure you have it right.

EDIT 2 - I just tried this in LTSpice:

Schematic:

Simulation:

There are two things to note here. One is the use of a gain slightly higher than 3 (R2 + R1)/R1 = 14.9k / 4.9k = ~3.04.
The other is the inclusion of "startup" in the .tran command. This tells it to start the supply voltages at 0, giving the oscillations a chance to start before the circuit has reached a steady state. Otherwise you would have to inject some noise into the circuit to simulate real world conditions. You should have a similar setting in MultiSim (e.g. "start supply voltages from 0" box to tick or something like that)

To include an AGC, you would use something like a thermistor in the feedback path (e.g. between R2 and ground) When the gain rises above 3, the thermistor passes more current and raises it's resistance, thus dropping the gain. You can also use a JFET, diodes, bulbs, etc. I wouldn't worry about this now though as you can get the circuit to work without this. The main purpose is to stop clipping/distortion of the sine wave which would be bad for e.g. a signal generator.

EDIT 3 - Limiting current with a resistor is not necessary, the TL071 will only draw as much current as it needs so you can connect it directly to the voltage source. The amount of current the supply could provide is irrelevant, the TL071 will draw max 2.5mA whether connected to a 5V 3mA supply or a 5V 300A supply.
To switch the power on and off, a P-channel MOSFET would work okay. You would tie it's source to +5V, drain to opamp V+ and gate to microcontroller pin. Set pin to 0 to turn on, 1 to turn off. If microcontroller supply is lower than 5V, then you would need a pullup resistor from gate to +5V (say 10k). Set pin to Hi-Z (e.g. input) to turn off, set to output and 0 to turn on.

EDIT 4 - An N-Ch MOSFET wouldn't work very well, as when you turn it on (e.g. gate to 5V), the source voltage rises and narrows the difference between the gate and source again. It will ultimately settle at around Vgate - Vt. So if the Vt (voltage required to turn on = threshold voltage) is say, +1.5V, and the gate is set to +5V then the source would only reach 5 - 1.5 = 3.5V. Since the source is connected to V+, then the opamp will only see 3.5V for it's positive supply.

Here is an example of the switching. Note how when the mcu pin (represented by V3) is set to 0 the oscillations start and vice versa:

Schematic:

Simulation:

The gain you measure depends on the amplitude of the signal in this circuit. This is the function of the diodes.

For example, if the output signal amplitude is small (say less than 0.6 V), then neither of the diodes across the resistor (R6 ? -- it's hidden) will conduct, and your gain will be 4x (with the 10k resistors). When the amplitude exceeds about 2.4 V peak, then at the extremes of the sinusoidal output, the diodes will conduct, and effectively limit the voltage across R6 to about 0.6 V. This reduces the gain beyond this amplitude to 3x (the other resistors control it).

If you were to draw a graph, the gain (slope of VOUT vs. VIN) would be 4x until the peaks reached 2.4 V, then would reduce to 3x for the portion of signal beyond that. Because gain changes with signal amplitude, you would get distortion.

This is the exact purpose of the diodes in this circuit -- they allow the gain to change, and if you get the resistors (and other components) right, for small signal amplitudes the overall lop gain will be just greater than 1, and oscillations will build up. However, when the amplitude reaches about 2.4 V, the gain will fall, and the amplitude will stabilize around where the 'average' gain is 1.0