**5. Conclusions**

In the present paper, we have developed a first-principles approach which allows one to calculate the local electric field in a nanocomposite capacitor and the parameters which characterize the electrical breakdown in it. It is found that for relatively low volume fractions of NPs (*f* ≤ 0.2), the breakdown voltage linearly decreases with *f* . The slope of this dependence is determined by the parameter *β* which is related to the NP polarizability.

A comparison with the available experimental data on the breakdown strength in polymer films doped with BaTiO3 NPs has revealed that the effective dielectric permittivity of NPs differs remarkably for different host polymers and is significantly lower than the values typical for ferroelectrics. These findings point at a dominant role of the interface polarization at the NP-polymer interface and an existence of a nonferroelectric surface layer.

**Author Contributions:** Conceptualization, V.B. and T.E.; funding acquisition, T.E.; investigation, V.B.; methodology, V.B.; project administration, T.E.; writing—original draft, V.B.; writing—review and editing, T.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is kindly supported by the IE Industrial Elektronik project (SFD-17-0036), which has received EU co-financing from the European Social Fund.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
