In Vedic astrology, the Sun is the principal of light, life and love, or true-will and perception. It is the most important factor for determining the spiritual life and potential of an individual. In represents the soul---the causal body or reincarnating entity---whose will is behind our fate. It is also the mind or the mental principal on a lower level as reason, discernment, clarity and illumination.

The following is the special name (nama) mantra for the Sun as preceded by it's Shakti or power mantra. It can be used to connect with the planetary deity and to energize all the higher powers of the Sun. 

The word 'Hrim' in above mantra denotes Harana Shakti, the power to hold, energize, attract and fascinate. (The word 'Hrim' should be pronounced as 'Hreem'.)

The following mantras are also considered very good for planet Sun. You may opt to recite one of the following mantra if you find it comparatively easy to remember.

The mantras are chanted on japa beads of 108 beads per string. They are similar to rosaries.

Recite the Sun's mantra for 7,000 times within 30 days. Once recitation is started, there should not be any break till the recitation are complete. Do 'Surya Namaskar' everyday early in the morning. begin recitation on a Sunday during the bright half of the Moon.

presence of 'Surya yantra' and/or 'Gayatri yantra' and/or 'Vishnu yantra' at the place of recitation may help you in achieving the desired results faster.

Gayatri Mantra for Sun:

"Om Asva dhvajaya vidmahe, pasa hastaya dhimahi, tanno Suryah prachodayat"

This Gayatri mantra consists of three parts. The first is the chants to the Sun. The second is the mantra proper. The third is a summary of the mantra's energies.

The Gayatri mantra is chanted at sunrise, noon and sunset. At dawn it is called Gayatri, the youthful form of the Goddess, consort of Lord brahma, the creator. It is called Savitri, the mature form, at noon, the consort
of Lord Shiva. It is called Sarasvati, the elderly form, at sunset, the consort of Lord Vishnu.

You may also opt to chant following Sun Mantra (7,000 times).

Japa kusuma-sankarsham kashyapeyam maha-dyutim
tamo-rim sarva-papa-ghnam pranato ' smi divakaram

"Let us chant the glories of the Sun God, whose beauty rivals that of a flower. I bow down to him, the greatly effulgent son of Kashyapa, who is the enemy of darkness and destroyer of all sins."